Bulletin BULLETIN of the ILLINOIS NATURAL HISTORY SURVEY HARLOW B. MILLS, Chief The Mayflies, or Ephemeroptera, of Illinois B. D. BURKS Printed by Authority of the STATE OF ILLINOIS WILLIAM G. STRATTON, Governor DEPARTMENT OF REGISTRATION AND EDUCATION VERA M. BINKS, Director NATURAL Hif^TORY SURVEY STATE OF ILLINOIS William G. Stratton, Governor DEPARTMENT OF REGISTRATION AND EDUCATION Vera M. Binks, Director NATURAL HISTORY SURVEY DIVISION Harlow B. Mills, Chief Volume 26 BULLETIN Article 1 The Mayflies, or Ephemeroptera, of Illinois B. D. BURKS Printed by Authority of the State of Illinois URBANA, ILLINOIS May 1953 STATE OF ILLINOIS William G. Stratton. Governor DEPARTMENT OF REGISTRATION AND EDUCATION Vera M. Binks, Diredor BOARD OP NATURAL RESOURCES AND CONSERVATION Vera M. Binks, Chairman A. E. Kmeknon. Ph.D.. fiioloty Walter H. New.iolse. Ph.D. Geo/ogy L H. Ti^kasv. Ph.D.. Foresirv Robert H. Anderson, B.b.C.E.. RtxKK Adams Ph D D Sc Chemistry hngineerin^ tVE;ust l.l 194.^. These females still carried their ej;;is. There is no locality where this species is known to breed within The length of nymphal life is so long and the nymphs are so frail that usually may- flies cannot be reared from eggs to adults without great loss of life. If mature or nearly mature nymphs whose wingpads show signs of darkening can be collected for the purpose of rearing, the number of deaths Fi({. 6. — Sip/ilonurus marshalli adult being removed from a rearing pan. a radius of 20 miles from Urbana. The most likely source of this typically large- river species was the Vermilion River, 30 air-line miles away, or the Wabash River in Indiana, almost 50 miles away. Rearing Mayflies Although the classification of the may- flies is based almost entirely on the adults, it is the nymphs which are most often taken in aquatic collecting or limnological work. In many instances, the generic and specific differences are much more distinct in the nymphs than in the adults. In order to be certain of their identity, it is necessary to rear the adults from the immature forms, but for most purposes of identification the association of mature nymph and adult is adequate. can be greatly reduced. Such nymphs are in the last instar, or at most only a molt or two removed from it. Mayflies which spend all or the latter part of their nymphal existences in still water can be easily and successfully reared from a late instar to the adult form in shallow pans. Such mayflies are CalUbactis, Siphlonurus, Lepiophlebia, Paralcptophlehia, Stenoiwma, Heptagenia, all the Caenidae, most Ephemeridae, and some species of Baetis. The rearing pans may be circular, flat- bottomed, enameled pans approximately 10 inches in diameter and 4 inches deep. A large, flat rock should be put in each pan and water from the place where the nymphs were collected added to a depth of not over 1 inch. The rock should be of a size to May, 1953 Burks: The Mayflies of Illinois 11 project partly above the water and thus provide a place on which an adult may emerge, fig. 6. A few rotting leaves or other detritus from the water where the nymphs were found should also be added to each pan to provide food. Care must be taken to have the pan, rock, and water all at the same temperature as the water from which the nymphs were collected. The nymphs may be taken from the pool or stream with a dipnet, or simply picked off rocks or other objects submerged in the water. They must be handled with the greatest care, as they are easily injured, always with fatal results. They may be kept in glass jars or cap vials partly filled with water until they can be transferred to the rearing pans. These temporary storage jars or vials must be kept cool, preferably by being partly immersed in the water where collecting is being done. An effort should be made to sort the nymphs to species, using the obvious charac- ters that can be seen with a hand lens. Part of each collection of a species should be preserved in alcohol at the time the other specimens are placed in the pans for rear- ing. An accession number should be given to each lot of specimens so that the adults, when secured, can unquestionably be as- sociated with their nymphs. The rearing pans containing the nymphs should be covered with a screen-wire or cheesecloth top to provide a place for the adults to rest after they have emerged and, also, to prevent their escape. The pans can be transported to any convenient and suit- able place for observation, but must be kept cool and protected from the direct rays of the sun. An outdoor, open-air insectary, if cool and shaded, is an ideal place for them. A cool basement also will serve. Many of the mayflies for this report were reared at the fish hatchery of the Illinois Department of Conservation at Spring Grove, Illinois. If more than a day or two elapses be- tween the time the living nymphs are col- lected and the time subimagoes begin to appear, it is advisable to change the water in the rearing pans. This can be done by dipping out part of the water in each pan and replacing it with aerated, unchlorinated water of the same temperature. When the subimagoes emerge, each speci- men should be removed to a cap vial or other similar glass jar in which one moderate- sized green leaf has been placed. The cap of this container must not make an air- tight seal. The subimago has to lose water during the subimaginal stage, but the loss must not be too rapid. The leaf will main- tain the humidity at a satisfactory level, while the loose cover on the container will permit the loss of water vapor by diffusion. If water is allowed to condense on the in- side of the container, the subimago will almost certainly die without shedding the subimaginal pellicle. The subimaginal skin will be shed usually within 24 to 36 hours, although, at very low temperatures, the subimago stage may last 2 or 3 days. When the adults emerge, they should be killed and mounted on pins. Notes should be made on the colors of the eyes and body of each specimen at the time of its death. The shed nymphal and subimaginal exuviae should be preserved in alcohol and be given the same lot accession numbers as the respective preserved nymphs. The reared adults should be studied care- fully to determine if all the specimens in each lot actually are of but a single species. The nymphs associated with each lot should also be studied critically at this time to determine if a pure culture of a single species is represented. The nymphs, the nymphal and subimaginal exuviae, and the adults should now be clearly and perma- nently labeled in such a way that there will never be doubts, in the future, as to the correct association of nymphal and adult specimens. Some mayflies, such as Isonychia, Ephem- erella, Ameletus, some species of Baetis, and Baetisca, cannot be reared successfully in pans. However, they can be reared in screen-wire cages partly submerged in the waters in which the nymphs live. When the subimagoes appear in these cages, they can be removed to cap vials, where the adults will emerge. The only real disad- vantage of this method is that it requires that much time be spent in the field and makes diflScult the finding of the shed nymph- al skins intact. Phillips (1930) was able to rear most of the New Zealand mayflies in laboratory aquariums, but I have had very poor results in my attempts to rear Illinois mayflies by this method. In the past, many associations of nymphs 12 Ii.i.iNois Natl'Rai. History Slrvey Bui.i.etin Vol. 26, Art. 1 and adults have been made by the process of relating adults taken by sweepinj: vegeta- tion around bodies of water with mature nymphs found in those waters at the same time. This method has led to so many misassociations that it should be followed only as a last resort, and the results should always be viewed with suspicion. Collectinji and Preserving Hoth nymphs and adults must be collected very carefully if intact specimens are to be secured. The most valuable adult speci- mens are those reared from nymphs. Rear- ing not only yields a definite association of the nymph and the adult form but makes possible a collection of well-preserved speci- mens. Collectinj: at lights will yield the largest number of adults. Although usually speci- mens taken at light traps are in very poor condition, some very worth-while Illinois records have been secured by these devices. Careful sweeping of the vegetation near bodies of water will yield much valuable adult material. Subimagoes secured by the same means should be placed in cap vials so that the adults can emerge a day or so later. Experience has shown that adult mayfly specimens are best preserved dry, on pins. Each specimen may be pinned through the thorax from dorsum to venter with the wings spread in the conventional manner for entomological specimens, or it may be pinned on the side, with the wings to the left, the pin being inserted through the pleura of the thorax. The latter method is the more rapid, and the specimens, al- though perhaps not so neat in appearance, are more easily handled for study and can be stored in smaller space. The wings may be spread during the dry- ing process, without the use of a conven- tional spreading board, in the following manner. A square piece of 50-pound ledger paper, as large as the maximum wing ex- panse, when placed on the pin above the specimen will serve to hold the wings out- spread at the proper angle during the 2 or 3 days required for drying. Another piece of the same weight paper of equivalent width, but twice as long, pushed up on the pin from below, will serve to hold the caudal filaments and fore legs at the proper ex- tension. Extremely small specimens, such as those of most species of Caenis, may be mounted on card points. If a long series of adult mayflies is avail- able, it is desirable to preserve some dry and some in ethyl alcohol. Dry specimens retain their color characters longer than those preserved in alcohol. Specimens I have seen that were collected by Benjamin I). Walsh of Rock Island, Illinois, and pre- served dry for more than 80 years show most of the color characters fairly well. In alcohol, the colors fade so rapidly that 10-year-old specimens in many genera are almost impossible to identify. Specimens in 85 per cent alcohol retain their color longer than those in 70 per cent alcohol, but, after storage in 85 per cent alcohol for several years, specimens become so hardened that it is almost impossible to make satisfactory slide mounts of the genitalia. Although alcohol is not satisfactory in some respects, it provides an easy method of preservation and permits compact storage of large series taken at one time and place, and, in some instances, is better for the study of structural characters. No matter how preserved, the adult speci- mens are extremely fragile and must be handled with the greatest care. Specimens, whether dry or in alcohol, should be stored so that they are not exposed to the direct rays of sunlight, as light quickly bleaches them. If it is ever desirable to preserve subi- magoes, they may be preserved in 70 per cent ethyl alcohol, as the colors of subi- magoes are usually unimportant. Then, at any later date, the adult genitalia of such specimens may be dissected out of the sub- imaginal pellicles and be cleared and mounted in the same fashion as those from any adult specimens. Nymphal specimens may be picked from rocks or other objects in the water or col- lected from the water itself by careful dipping with an aquatic dipnet. In running water, large numbers of specimens may be secured if a seine or dipnet is held in the current and the rocks, gravel, and other objects on the bottom upstream from the net are carefully turned over. The nymphs will release their holds on these objects and the current will carry them into the net. Nymphs and exuviae are best preserved in 70 per cent ethyl alcohol. Preserving mixtures containing acetic acid or glycerin May, 1953 Burks: The Mayflies of Illinois 13 should be avoided, as they eventually make the specimens so soft that the parts will not hold together. Glycerin also eventually turns mayflies almost pitch black. Formalin hardens specimens so much that it should not be used. Collections of specimens in alcohol, if in vials with cork stoppers, will almost certainly have many losses due to evaporation of the alcohol. The use of red rubber stoppers in the vials will greatly reduce evaporation, but. even with the best care, specimens will occasionally be found to have dried out. Many dried specimens can, however, be partially restored by careful treatment with trisodiumphosphate (Van Cleave & Ross 1947). This method of restoration often makes it possible to identify nymphs which formerly had to be discarded. Study Preparations For a study of the male genitalia, slide mounts of these structures must be pre- pared with special care. I have used the following procedures in material examined in this report. The entire mayfly is first relaxed and the caudal filaments removed but saved in case it should be necessary to study them later. Then the apex of the abdomen is cut ofi and cleared in cold 10 per cent potassium hydroxide for a period of 6 to 12 hours. After this treatment the dis- section is placed in distilled water and any undisintegrated muscle or abdominal con- tents are carefully teased out with fine dissecting needles. The preparation is transferred first to 50 per cent ethyl alcohol and then through two changes of 70 per cent alcohol, being left in each not less than 15 minutes. A few drops of acidulated acid fuchsin are added to the last change of 70 per cent alcohol, and after a minimum of 15 minutes the preparation is removed to 95 per cent alcohol. In this alcohol the tenth tergite and the bases of the caudal filaments are dissected off so that they will not obscure the structure of the penis lobes in the finished slide. The genitalia are then left in the 95 per cent alcohol until all excess stain has been washed away. The preparation is mounted, directly from the 95 per cent alcohol, in balsam. The latter is a special medium made by diluting standard, filtered Canada balsam with 10 per cent turpentine. A small drop of this medium is put on the slide and the stained genitalia preparation placed in it; the trans- ferring is done with a hooked dissecting needle, not a pipette. This turpentine mounting medium dries slowly enough to allow ample time for orienting the dissection correctly on the slide. Each specimen is mounted with the genital forceps down, care being taken to mount all dissections as nearly as possible in the same position, for the structures of the penis lobes of a single species may look quite different if seen from different angles. The preparation is then placed in a dust-tight box to dry. It should be examined at intervals over a period of several days and the dissection straightened, if necessary, with a dissecting needle. The coverslip is not put on until the preparation is almost completely dry. In this paper, the drawings of the male genitalia were, except in Leptophlebiidae, made from the dorsal aspect, that is, with the penis lobes above the genital forceps. In the Leptophlebiidae, the genitalia were drawn from the ventral aspect, so as better to show the ventral appendages of the penis lobes. In many instances, it is necessary to make dry mounts of the adult wings so that the venation can be studied critically. If the adult specimen is preserved in alcohol, the mount can be made directly, but, if the specimen is dry, it must first be relaxed. The wings from the alcoholic specimen or relaxed dry specimen are then carefully dissected off with dissecting needles or knives. As these wings are extremely fragile, the operation must be done with great care. The wings can easily be re- moved by severing the muscles at the base of each wing. The detached wings are carefully washed in a watchglass containing 70 per cent alcohol to remove any dust or debris. It may be necessary to use a fine camel's-hair brush to remove all the dust; the brushing must be done very carefully, else the fragile wings will be torn. Next a drop or two of 70 per cent alcohol is placed on a clean microscope slide and the wings are floated onto it. They should be spread and arranged symmetrically, dis- secting needles being used for the manipu- lation. Then, before the alcohol evaporates, a square. No. 1 thickness coverslip is put on. Coverslips three-fourths inch or seven- 14 Ii.iiNois Natlrai. History Slrvev Bulletin Vol. 26, Art. 1 oighths inch square will serve for most mayHy u injjs. The weight of this coverslip will serve to hold the wings flat and in place as the alcohol evaporates. When most of the alcohol has evaporated, but the wings arc still slightly damp, a narrow strip of gummed paper is moistened and affixed along each of the lateral margins of the coverslip. The strips of paper serve to hold the coverslip in place during the drying process. After the mount is com- pletely dry (it is best to let the preparation stand 24 hours to be sure it is dry), strips of gummed paper are affixed to the top and bottom margins of the coverslip to make a permanent mount. Ciummed paper having animal glue should be used, as it can be relied upon to adhere tightly to the polished glass surfaces for years. These slide preparations may then be studied and stored, as afe the balsam mounts of the genitalia. They must, however, always be handled carefully, as the wings are most fragile after they are thoroughly dry. Literature The mayflies, in contrast with many other insect groups, are fairly well known for the world as a whole. The great majority of specimens of adults from anywhere in the world can be placed generically with the keys of Ulmer (1933, 1939). Generic keys to the nymphs of the world are not so readily available, but Ulmer (1940) keyed out many nymphs, and most of the faunal papers cited below include keys to nymphs as well as adults. The excellent monograph of Eaton (1883-1888) still serves for the generic and specific identifica- tion of the adults and nymphs of many forms from all parts of the world. A great many papers have been published which include keys and descriptions of the species of a single country or region. Klapalek (1909), Ulmer (1924fl), and Schoenemund (1930) published keys and descriptions for the German and central European species of mayflies. Kimmins (1942) treated the British species, Perrier (1934) the French, Grandi (1941-1951) the Italian, and Lestage (1928 et seq.) the Belgian. Chernova (1940) described and keyed the nymphs of the Russian species. Barnard (19.?2, 1940) published on the South African species, Lestage (1925i) cataloged and described part of the North African species, and Ulmer (1930) published a paper on some Abyssinian species. Chopra (1927) published a comprehensive paper on the Indian species, while Traver (1939) considered species endemic to the Himalayan region. Phillips ( 1930) published a revision of the New Zealand species. Ulmer (1924f, 1939-1940) described the East Indian and Philippine species, Lestage (1921, 1924Z') treated the species of Indo-China, while Ulmer (1926fl) published a large paper on the species of China, and Ueno (1931) treated those of the Japanese fauna. Traver (1938) published a work on the mayflies of Puerto Rico; she also (1944) treated many of the species of Brazil. Ul- mer (1938) treated the Chilean species. Needham & Murphy (1924), Ulmer (1942- 1943), and Traver (1946-1947) published major contributions on the South American and Central American species. Spieth (1943) made some taxonomic notes on several species from Surinam and other Neotropical localities. The majority of the species of mayflies occurring in North America north of Mexico can be identified with the keys and de- scriptions of Traver (1935a). Despite the fact that some of the keys and many of the descriptions in her paper were compiled from the literature, and that various other work- ers have not agreed with her conclusions on a number of points, her work neverthe- less remains the greatest single contribution yet made to the study of North American mayflies. This paper is especially valuable in that it brings together the great number of descriptions of North American species that appeared in the nearly 50-year period between 1888 (the time that Eaton's mono- graph was published) and 1935. McDun- nough (1921-1943) published a long series of extremely valuable papers containing descriptions and illustrations of a great many of the North American species of mayflies. Berner (1940-1950) studied and keyed out the Florida species. This list of works just cited does not, of course, constitute a complete bibliography of the world literature on mayfly classifica- tion, but it will serve to indicate the present extent of the comprehensive literature. The Walsh Species Benjamin D. Walsh became interested in mayflies and related insects about the year Mav, 1953 Burks: The Mayflies of Illinois 15 Table 1.—Mayfly species described by Benjamin D. Walsh in 1862 and 1863. and status of lectotypes designated by Nathan Banks from specimens collected by Walsh and deposited by Herman A. Hagen in the Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts. Walsh Species MCZ TvpE No. Condition Label Species Described in 18 Baetis sicca Potamanthus odonatus* Palingenia vittigera* Palingenia flavescens Palingenia pulchella Palingenia terminata Ephemera flaveola Ephemerella excrucians Ephemerella consimilis* Cloe Jerruginea * Cloe fluctuans* Cloe dubia Cloe tnendax Species Described in 1863 Baetis interlineata Pentagenia quadrip u ndata "* lleptagenia simplex Heptagenia cruentata* Heptagenia maculipennis Ephemera myops Cloe propinqua 11248,0^ Good 11252, 11251, 16 ii i.iNois Natural History Survey Bulletin Vol. 26, Art. 1 Hat:cn did not return Walsh's liiiplicate specimens to him. hut added them to his own collection. Walsh sent specimens of additional species to Ha^en in 1864; these Haj;en added to his collection. Later, in 1870. Ha^en hroujjht his collection to the United States and deposited it in the .Mu- seum of Comparative Zoolojzy. Harvard L'niversitv. In the meantinir, Walsh had died, in 1869. and his collection, containinji the types of all his mayflies, was deposited in the Chicago Academy of Sciences. In 1871, this collection was completely de- stroyed in the great Chicago fire. As a result, the specimens of Walsh's species in the Hagen collection, still preserved at the .Museum of Comparative Zoology, hccame the sole remaining authentic representatives of those species. It should be noted that, although the true types of Walsh's species are destroyed, n.ost of the specimens of W^ilsh material now in the .Museum of Comparative Zoology may be considered to be cotypes. Some specimens, however, were collected by Walsh after the descriptions were published, as is shown by the specimen labels, and these specimens are only autotypes. Lectotypes for most of Walsh's species of mayflies have been designated by Nathan Banks. A number of workers, myself included, have studied these specimens. Table 1 gives a list of the species described by Walsh and the present status of the lectotypes. In addition to the species listed in table 1, the Museum of Comparative Zoology collection includes specimens determined and labeled by W^alsh as Baetis arida Say, B. alternata Say, Potamanthus cupidus Say, Paitngenia itmhata Pictet, Paliugciiia hilin- eata Say, Palingcnia intcrpunctata Say, and Battisca obesa Say. All were collected by Walsh at Rock Island. In collecting material for the present Illinois report on mayflies, we made a great effort to secure good series of all the Walsh species from the type locality. The results were somewhat disappointing, as, of the 31 species described or identified by Walsh, we were able to secure only 8 at Rock Island, even with intensive collecting. This is not surprising when it is realized that the rivers around Rock Isl.-'nd are now quite different than they were in Walsh's time. In the 1860's the Mississippi and Rock rivers at Rock Island were large, rapid rivers (Walsh 1863:202). Since Walsh's time, extensive dredging, channel straightening, and dam- ming operations have greatly reduced the rapidity of flow of these rivers. As a result, the Mississippi River at Rock Island is now ecologically more like a lake than a rapid river, and the Rock River is extremely sluggish. Changes in the rivers have pro- duced a corresponding change in the local mayfly fauna. In Walsh's time, also, it was the annual practice, in spring, to float log rafts down the Rock and .Mississippi rivers to the saw mills located in Rock Island (Walsh 1862: il2\ 186.^:202). These rafts originated in the pine forests of Wisconsin and Minnesota. Walsh noticed that large numbers of mature mayfly nymphs were brought down the river to Rock Island with these rafts. The nymphs, in the accumulated debris of the rafts, crawled out on the logs to molt. Walsh collected much of his material from these log rafts. Needless to say, this source of specimens long since has disappeared from Rock Island. Although we collected only 8 of Walsh's species at Rock Island, we ultimately secured 27 of his 31 species by searching in other localities. Most of the specimens we took at various points on the Rock River upstream from Rock Island, notably at Prophetstown, Dixon, Sterling, Oregon, and Rockford. Some also we took in southern Illinois at Mount Carmel, on the Wabash River. Of the Walsh species which have not been collected again in Illinois, Ephemerella excrncians has recently been reared in northern Michigan (Leonard 1949:158). E. consim'dis, based on a very brief, com- parative description, and unrepresented in the Museum of Comparative Zoology col- lection, has of necessity remained unrecog- nized. Walsh identified Rock Island speci- mens as questionably belonging to two species described by other authors: Baetis debilis Walker and Cloe utiicolor Hagen. The former has been shown by Eaton (1885: 253) to be a misidentification, but exactly what species Walsh had cannot now be determined. The latter was an identification of a Hagen species which is itself unrecog- nizable today. As we lack the original material, what species Walsh ascribed to the name unicolor cannot be ascertained with any degree of certainty. May, 1953 Burks: The Mayflies of Illinois 17 External Morphology The external features of both nymph and adult mayfly are described in detail in The Biology of Mayflies (Needham et al. 1935). Only those characters used in identification of Illinois species are mentioned here. Many of the morphological structures which have proved useful in classification are shown in fig. 7 of a generalized mayfly adult and in fig. 8 of a generalized nymph. The terminology for the adult thorax is essentially the same as that used by Velma Knox (1935). The location of the various margins and areas of the wings is illustrated in figs. 7 and 9. The disc of the wing is the middle part, bounded roughly anteriorly by R^ and posteriorly by Cu, but not in- cluding the marginal or extreme basal areas. The spines on various parts of the penis valves which have proved of diagnostic value, and their locations, are shown in fig. 10, of the generalized male genitalia. All mayfly nymphs are strictly aquatic and respire by means of gills, which vary greatly in size and form in different species. Typically, there is one pair of gills on each of the first seven abdominal segments. They may be lamelliform (platelike), filiform (threadlike), or a combination of these two forms, figs. 51-55, 9\a-d, 96, 113, 172, 199, and others. When mayflies first emerge as winged insects, in the subimago stage, the surfaces of the semiopaque wings are covered with microtrichia ; the wing margins and the caudal filaments are clothed with numerous long, slender setae. Beneath the subimaginal pellicle the adult eyes, legs, genitalia, and caudal filaments can be seen, contracted and wrinkled. Most mayflies remain in this stage about a day before shedding the sub- imaginal pellicle. Immediately following, the legs in most species and the caudal filaments become greatly lengthened and the eyes of the males greatly expanded ; the wings are clear and hyaline, and they lack microtrichia and marginal setae. In a few mayfly adults, the legs are aborted, while, in some others, they are so greatly reduced as to be useless. Although mayflies typically have two pairs of wings, the anterior pair being much the larger, there are some species in which the hind wings are lacking. In most adults, the compound eyes occupy the greater part of the head and, in the males of most species, the eyes are larger and closer together on top of the head than in the females. In the males of some genera, the eyes are greatly expanded and each is divided into an upper and lower portion, which may be further differentiated by size and color, figs. 255-257. In the nymphs, the compound eyes show a considerable range in size and position but none shows the high degree of development exhibited in adults. The colors of the com.pound eyes of the male as given in the species descriptions and keys are those of the eyes while the specimens were still alive or had been dead only a short time. In mayflies, such as Baetis, which have divided eyes, the color of the upper portion of each eye is the sig- nificant one ; the lower portion, as is well known, is a day-eye, with pigmentation so extensive that this part of the eye appears black. In such forms as Stenonema and Heptagenia, occasional specimens are to be found in which the entire eye is completely black, before death as well as after. These specimens should be disregarded, as this blackening is apparently due to the corneal layer of the eye separating from the hypoder- mis. After specimens have been killed and are thoroughly dry, the colors the eyes had in life disappear completely. The other color characters as given in the descriptions in this report are, wherever possible, those of fresh, dry specimens. All colors fade or change somewhat within a few days after death of the specimens, re- gardless of the method of preservation; however, this loss of color is relatively slight in dry specimens stored away from the light. Specimens preserved in 70 per cent alcohol soon change color almost completely, becoming, after a few months, only a dull tan or yellow, even though the color in life may have been of various shades from dark brown to white. On dry specimens, the salient features of the color pattern are relatively permanent, but the delicate tints of red, green, gray, or yellow of fresh specimens eventually disappear or become scarcely discernible. The system of nomenclature for wing veins used by Traver (1935^:119) has been followed in this report. It may be noted that this differs from the system of Tillyard (1923) in several respects. For instance, the branched, convex vein in the center of the fore wing called MA by Tillyard 18 Illinois Natural History Survey Bulletin Vol. 26, Art. 1 is calird R^s in this report. The branches have been named .M, and M.^ by Ulmer (19.?-?, pis. I, II) and 6 and 6' by Eaton (188.?. pis. I-XXIII). The vein R^+s is of greatest importance, as it is the best land- mark that can be used in identifying the veins of the mayfly fore wing. Once it has been located (except in the greatly special- ized Oligoneuriidae) , all other veins anterior and posterior to it can quickly be located. Traver considered R4+5 to be a branch of Rg, whereas Tillyard believed it to be a marginal --intercalary PU- 7.—Generalized mayfly adult male, showing structures used in classification. May, 1953 Burks: The Mayflies of Illinois 19 branch of M. Actually, as good a case can be made for considering this vein a branch of Rg as of M. It is not clearly joined to either, but sometimes appears to arise nearer the stem of R than of M. The poorly de- veloped axillary sclerites of the mayfly wing give no conclusive evidence either way. Such being the case, I have decided to follow Traver's system, in which this vein is con- sidered to be a branch of Rj, as her system was used consistently in The Biology of Mayflies (Traver 1935a). This work has been, and is most likely to continue for many years to be, the standard reference work on North American mayflies. It should further be noted that the veins called Mj and M., by Traver have been called Cu^ and Cu,,'by Ulmer, MP by Till- yard, and branches of vein 7 by Eaton. The veins Cu^ and Cu„ of Traver's system cor- respond to 1st and 2nd anal veins of Ulmer's, Cuj and Cu^ of Tillyard's, and veins 8 and 9 of Eaton's. In mayfly literature, it is frequently stated opical 'angle genital forceps .forceps base Fig. 8.—Dorsal aspect of generalized mayfly nymph, showing structures used in classification. Fig. 9.—Generalized mayfly wings, showing principal veins and areas used in classification. Fig. 10.—Generalized mayfly male genitalia, showing structures used in classification: a, discal spines; b, subapical spines; c, apical spines; d, apicomesal spines; e, lateral spines; f, basal spines; g, mesal spines. 20 li.i.iNois Natlrai. Historv Slrvey Bulletin Vol. 26, Art. 1 that the median caudal Tilament is wanting, but actually this filament is simply reduced to a minute, unse;imented or partly seg- mented vestige. In all adult mayflies there is at least some indication of it. The outer caudal filaments are the cerci. An arbitrary system for the designation of sizes of specimens has been followed in this report. The size of an adult specimen is taken to be the length of the body with- out the head or fore legs and without the caudal filaments. Specimens having such a body length of 5 mm. or less are called small, those from 6 to 10 mm. long are called medium, and those over 1 cm. long are designated as large. The length of the body in nymphs is without the head or caudal filaments, and the sizes given refer to mature nymphs, that is, ones with dark wingpads. Identification of Sexes The adult male mayfly is easily recog- nized by the presence of a pair of forceps, or claspers, near the apex of the ninth sternite, as well as by two shorter structures, the penes, between the arms of the forceps. The forceps, except in the subfamily Camp- surinae, are segmented, and both forceps and penes vary greatly in size and form, figs. 60-67. These same structures can be seen through the pellicle of the subimago and of the mature nymph, although in these two stages they are soft and less sclerotized than in the adult. They are not fully ex- panded in the subimago, and much less de- veloped in the nymph. In the female, the posterior margin of the ninth abdominal sternite is rounded, simple, and without prominent processes or addi- tional structures. In a few genera, the female possesses a rudimentary ovipositor. Classification The order Ephemeroptera is one of the most archaic of winged insect groups. It is not closely related to any other order but, as Tillyard (1917) points out, certain points of resemblance give some slight evidence of a very ancient connection with the Odonata. These points of resemblance, not common to other orders, are the presence of only one wing axillary, the inability to fold the wings backward or downward over the abdomen, and the retention of abdominal gills in Ephemeroptera and in a few primitive nymphs of Odonata (Cora and Pseudo- phaea). The fossil record indicates that the two orders were already differentiated in the Upper Carboniferous Period but were then more closely related than thev are today (Tillyard 1917:6). At the time Eaton wrote his Revis'iotial Monograph (1883-88), the mayflies were considered to constitute the single family Ephcmeridae. However, several years earlier Eaton (1869:132) had indicated that the family Ephemeridae could be sub- divided into three major divisions, based on the habits and structures of the nymphs: (1) the burrowing forms with tusked man- dibles, (2) the flat, crawling forms, and (3) the rather long, slender, free-swimming forms. In the Revisional Monograph, he divided the adults into three groups; these groups somewhat paralleled the divisions he had previously suggested, based on the nymphs. He further subdivided these three groups into 13 generic types; the three groups were not named as taxonomic cate- gories. Banks (1900:246) published a classifica- tion of the mayflies, considering them to represent but the one family Ephemeridae, but dividing this family into seven tribes: Baetiscini, Polymitarcini, Leptophlebini, Siphlurini, Ephemerini, Baetini, and Caenini. Needham (1901:419) published a key to the nymphs of the family Ephemeridae and indicated that this family could be divided into three subfamilies, the Ephemerinae, Heptageninae, and Baetinae. Needham mentions (1905:29, footnote) that this key indicated subdivisions of the Ephemeridae into subfamilies which were very similar to those given in a manuscript key prepared earlier by C. A. Hart for use by students at the University of Illinois. A few years later, Needham (1905:22) published a revised key to the family Ephemeridae in North America. In this key, which included both nymphs and adults, he again divided the Ephemeridae into the three subfamilies Ephemerinae, Hepta- geninae, and Baetinae. These three sub- families corresponded only very roughly to the three groups into which Eaton had di- vided the family Ephemeridae in his classi- fication. Klapalek (1909) then published a greatly expanded classification of the mayflies, based on German species, dividing the order into May, 1953 Burks: The Mayflies of Illinois 21 10 families; Palingeniidae, Polymitarcidae, Ephemeridae, Potamanthidae, Leptophle- biidae, Ephemerellidae, Caenidae, Baetidae, Siphlonuridae, and Ecdyonuridae. These families he placed in the order Ephemcrida. It may be noted that Klapalek's classification bears considerable resemblance to the earlier classification of Banks (1900:246), and, as Ulmer (1920fl:98) remarks, the 10 families in Klapalek's classification correspond almost exactly to 10 of the unnamed subdivisions of the family Ephemeridae that Eaton had indicated in his monograph. Ulmer (1914), in a new classification of the German mayflies, added the family Oligoneuriidae. Bengtsson (1917) added the family Ame- tropidae to the classification and changed the name of the Ecdyonuridae of Klapalek's classification to the Heptageniidae. The same year, Lestage (1917) published a classification of the Palearctic mayfly nym.phs in which he used only the families Ephemer- idae, Heptageniidae, Baetidae, Oligoneuri- idae, and the new family Prosopistomatidae. Three years later, Ulmer (1920^:99) published a revised classification for the mayflies of the world in which he combined the essential features of all the preceding classifications. He elevated the three sub- families of Xeedham's classification to sub- orders, with 14 families beneath them, but no subfamilies. Ulmer's classification was arranged as follows: Suborder Ephemeroidea Family Palingeniidae Family Polymitarcidae Family Ephemeridae Family Potamanthidae Suborder Baetoidea Family Leptophlebiidae Family Ephemerellidae Family Caenidae Family Baetidae Family Oligoneuriidae Family Prosopistomatidae Suborder Heptagenioidea Family Baetiscidae Family Siphlonuridae Family Ametropodidae Family Ecdyonuridae ( Heptageniidae) A few years later, Handlirsch (1925: 415) published a much more conservative classifi- cation for the mayflies of the world. In this he placed all the forms in one family, but employed a number of subfamilies and tribes, as follows: Family Ephemeridae Subfamily Siphlurinae Tribe Siphlurini Tribe Ametropodini Tribe Ecdyurini Subfamily Baetiscinae Subfamily Prosopistomatinae Subfamily Baetidinae Subfamily Caenidinae Subfamily Leptophlebiinae Tribe Ephemerellini Tribe Leptophlebiini Subfamily Ephemerinae Tribe Ephemerini Tribe Potamanthini Tribe Polymitarcini Tribe Palingeniini Subfamily Oligoneuriinae Ulmer (1933) later revised his classifi- cation of 1920 but made no changes in the arrangement of suborders and families. The same year, Spieth (1933) published a paper on the phylogeny of mayflies. His con- clusions, based on a study of adult wings and male genitalia and nymphal gills and mouthparts, were that the North American mayflies represented four superfamilies and eight families, as follows: Superfamily Siphlonuroidea Family Siphlonuridae Family Heptageniidae Family Baetidae Superfamily Ephemeroidea Family Leptophlebiidae Family Ephemeridae Family Ephemerellidae Superfamily Caenoidea Family Caenidae Superfamily Baetiscoidea Family Baetiscidae Two years later. The Biology of Mayflies (Needham et al. 1935) appeared. In this work the mayflies were divided into three families (the three subfamilies of Needham's earlier classification) and 17 subfamilies: Family Ephemeridae Subfamily Palingeniinae Subfamily Ephoroninae Subfamily Ephemerinae Subfamily Potamanthinae Subfamily Campsurinae Subfamily Neoephemerinae Family Heptageniidae Subfamily Heptageninae 22 Illinois Natlrai. History Survey Bulletin Vol. 26, Art. 1 Family Bactidae Subfamily Olinoncurinae Subfamily Ametropinae Subfamily Mctrctopinae Subfamily Siphlonurinae Subfamily Baetiscinae Subfamily KphcmtTellinar Subfamily Leptophlebiinai- Subfamily Cacninae Subfamily Baetinac Subfamily Prosopistomatinac The superjiencric classification of the mayflies which I have adopted here does not coincide exactly with any of the previous classifications, although it more closely aprees with the classification of Banks (1900) than with that of any other author. I do not believe that all mayflies can be divided into only three main categories with- out introducing an unjustifiably large num- ber of exceptions into the characterization of each of those three main divisions. Al- though the mayflies are an extremely archaic group, we still have living representatives of many of the diverse branches that have arisen within the order during its long history. As has been shown by Tillyard (1925, 1932), the mayflies reached their maximum abundance in the Permian Period and have declined since. In the long period from the Permian to the present, many quite distinct types of mayflies have arisen, all of which evidently represent considerable di- vergence from the Permian mayfly prototype. Characteristics of this ancestral mayfly type are discussed by Tillyard (1932) and Carpenter (1933). In our present-day mayfly fauna, we re- tain representatives of many of these diverse lines of mayfly evolution. The family classi- fication should, as much as possible, reflect these degrees of divergence from the an- cestral mayfly prototype. Certainly there are more than 3, and, in my opinion, there are at least 11 distinct lines of descent. I have accordingly distributed our Illinois mayflies among 10 families; the eleventh, Prosopistomatidae, is not represented in North America. This family classification has been arrived at through an evaluation of all available characteristics in nymphs and adults. The conspectus of the supergeneric classification followed here is given below: Order Ephemeroptera Family Ephemeridae Subfamily Campsurinae Subfamily Potamanthinae Subfamily Ephoroninae Subfamily Ephemerinae Subfamily Palingeniinae Family Neoephemeridae Family Caenidae Family F'phemerellidae Family Baetiscidae Family Prosopistomatidae Family Oligoneuriidae Family Leptophlebiidae Family Baetidae Subfamily Siphlonurinae Subfamily Isonychiinae Subfamily Baetinae Family Ametropidae Family Heptageniidae It must be admitted that varying degrees of relationship are indicated among some of these families. The Caenidae almost cer- tainly arose from an ephemerid ancestor, as is shown by the still existing but ex- tremely rare interstitial forms which are placed here in the Neoephemeridae. The point of divergence, however, of the Cae- nidae from the ephemerid stem must have been quite remote. The Ephemerellidae, Oligoneuridae, Baetiscidae, and Prosopisto- matidae apparently have no near relatives in the recent fauna. The Leptophlebiidae possibly arose from the same stem which produced the Baetidae, although the simi- larity between the two is slight. On the other hand, the Heptageniidae and the Baetidae must have arisen from an ancestor common to both of these families; the rare but still existing interstitial forms between these two families indicate this probable relationship. The forms here included in the Baetidae admittedly represent rather widely divergent types. The Siphlonurinae contain quite archaic forms that (Spieth 1933:329) prob- ably arose very early from the Permian mayfly prototype, while the Baetinae con- tain greatly reduced adult forms that prob- ably arose much later. The baetine and siphlonurine nymphs are, however, quite similar, and most adult baetine structures can be derived by simple reduction from corresponding adult structures in the Si- phlonurinae. The divided compound eyes of the adult male baetines, on the other hand, seem to be strikingly different from the eyes of the siphlonurines, but actually the begin- nings of the development of this divided eye Mav. 1953 Burks: The Mayflies of Illinois 23 f^^ ^=^^^=^ Fig. 11. — Caenis simulans, hind leg of adult male. Fig. 12. — Brachycerciis lacustris, hind leg of adult male. Fig. 13. — Tricorythodes atratus, hind leg of adult male. Fig. 14. — Neoephemera purpurea, hind leg of adult male. Fig. 15. — Callibaetis fluctuans, hind leg of adult male. Fig. 16. — Ephemerella needhami, hind leg of adult male. Fig. 17. — Stenonema pulchellum, hind leg of adult male. FijJ. 18. — Isonychia sicca, hind leg of adult male.. Fig. 19. — Heptagenia sp., hind leg of adult female. Fig. 20. — Siphlonurus alternatus, hind leg of adult female. Fig. 21. — Leptophlebia nehulosa, hind leg of adult male. Fig. 22. — Siphloplecton interlineatum, hind leg of adult male. Fig. 23. — Ephoron leukon, fore leg of adult male. Fig. 24. — Ephemera simulans, fore leg of adult male. Fig 25. — Siphloplecton interlineatum, hind leg of mature nymph. Fig. 26. — Ameletus lineatus, hind leg of mature nymph. Fi^. 27. — Ilfxagenia bUineata, wings. Fig. 28. — Nioephemera purpurea, wings. Fig. 29. — Ephemcrella lutiilenta, fore wing. Fig. 30. — Baetisca obesa, fore wing. . Fig. 31.—Ba^-m /.ro/zwywMj, fore wing. winf ?Af7erTiT"' ^''^*'"^^""^'"'^"^"' fore Fig. ZS.-Paraleptophlebia praepedita, pos- P^^ ^1 ^w ' , t^'"'"'" half of fore wing. (Ait V^^nr"""'"' '""""'^^' f"--^ ^i"K. Fig. 2,6.-1Sonychia rufa, posterior half of C-! 71 c"- /, , , '^"'e wing. of for'e whit'^ ^ "" "''''• ^°''"'"' ^"'^ ^'^- 37.-5///;/o;n/r». ry„r/..r.«./., posterior *' half of fore wing. Mav. 1953 Burks: The Mayflies of Illinois 25 Fig. 38. — Ephoron leiikon, fore wing. Fig. 39. — Ephoron leukon, hind wing. Fig. 40. — Pentageriia I'ittigera, fore wing. Fig. 41. — Pentagenia vittigera, hind wing. Fig. 42. — Potamanthus verticis, fore wing. Fig. 43. — Potamant/ius -verticis, hind wing. Fig. 44. — Tortopus primus, fore wing. Fig. 45.— Tortopus primus, hind wing. Fig. 46. — Ephemera simulans, fore wing. Fig. 47. — Ephemera simulans, hind wing. 26 Illinois Natural History Survey Bulletin Vol. 26, Art. 1 can be sfen clt-arlv in the living adult male siphlonurines. KEY TO FAMILIES .Adults 1. Lateral ocellus in both sexes extremely lar^e in comparison with a compound eye; each ocellus approximately one- half as large as a compound eye Caenidae, p. 43 Lateral ocellus in males never more than one-tenth as large as a compound eye; in females lateral ocellus not more than one-fourth as large as a compound eye 2 2. Vein Sc of fore wing wanting or united with R,, figs. 32, 33 Oligoneuriidae, p. 79 Vein Sc of fore wing present as a separate vein extending from base to apex ot wing, figs. 27-31 3 3. Cubital intercalary veins entirely absent, crossveins in disc of fore wing weak and netlike, fig. 30 Baetiscidae, p. 75 Cubital intercalary veins present, cross- veins in disc of wing not netlike, figs. 27-29,31 4 4. Hind tarsus with five clearly differentiated segments, true first tarsal segment not fused with tibia, figs. 17, 19 Heptageniidae, p. 151 Hind tarsus with only three or four clearly differentiated segments, figs. 14-16, 18, 20-22 5 5. Vein M2 of fore wing sharply bent near base, figs. 27, 28, running parallel with vein Cui in this area 6 Vein M2 of fore wing straight throughout its length, figs. 30, 31, 34-37, or curved no more than in fig. 29 7 6. Costal crossveins of fore wing in area basad of bulla partly or almost com- pletely atrophied; veins Mi and M2 of hind wing separating distad of the center of wing; fig. 28 Neoephemeridae, p. 42 Costal crossveins in both fore and hind wings well developed; veins Mi and Mo of hind wing separating proximad of center of wing; figs. 27, 38-47 Ephemeridae, p. 27 7. Fore wing with one or two long intercalary veins between Mo and Cui, fig. 29 . Ephetnerellidae, p. 55 Fore wing without long intercalaries be- tween veins M2 and Cui, figs. 34—37. , 8 8. Vein Cu2 of fore wing angularly bent toward inner wing margin, figs. 35, 185-192 Leptophlebiidae, p. 81 Vein Cuo of fore wing straight or evenly curved, figs. 31, 34, 36, 37 9 9. Cubital intercalary veins of fore wing consisting of one or two pairs of long, parallel veins, free marginal veinlets always absent, fig. 34; hind wings in- variably present Ametropidae, p. 144 Cubital intercalary veins of fore wing either a series of short, slightly sinuate veins extending from vein Cui to inner wing margin, figs. 36, 37; or cubital in- tercalaries one or two long, basally de- tached veins accompanied by free marginal veinlets, figs. 31, 220-222; hind wing sometimes absent Baetidae, p. 97 Mature Nymphs 1. Gills on abdominal segments 1-6 con- cealed under carapace-like projection of thoracic notum, fig. 181 Baetiscidae, p. 75 Abdominal gills not concealed under cara- pace-like projection of thoracic notum . . 2 2. Second abdominal segment bearing a pair of operculate or lidlike gills which cover gills on segments 3-6; gills lacking on segment 7; figs. 88, 96, 113, 114. . . . . .3 Second abdominal segment not bearing a pair of operculate gills which cover more posterior gills; operculate gills, if pres- ent, borne by segment 4; gills present on segment 7 4 3. Operculate gills fused on meson, connate; a hooklike, median spine at posterior margin of abdominal tergites 6-8, fig. 88 Neoephemeridae, p. 42 Operculate gills not fused on meson; ab- dominal tergites 6-8 without hooklike spines, figs. 96, 113, 114 Caenidae, p. 43 4. Gills of first abdominal segment large and situated on the venter, fig. 184 Oligoneuriidae, p. 79 Gills of first abdominal segment dorsal, or first abdominal segment without gills. . 5 5. Gills always absent from second abdomi- nal segment and sometimes absent from third segment, also Epiietnerellidae, p. 55 Gills present on abdominal segments 1-7..... _ 6 6. Tibia of hind leg shorter than hind tarsal claw, figs. 301, 312; or claw at least six times as long as wide at its widest point, fig. 25 Ametropidae, p. 144 Tibia of hind leg as long as, or longer than, hind tarsal claw, figs. 26, 247, 254, 266, 385; claws relatively thick 7 7. Each mandible with a projecting tusk, visible from dorsal aspect, figs. 2, 55, 59.. _ _ _. . ._ 8 Mandibles without projecting tusks. . 9 8. Gills relatively broad, biramous, with margins ciliate, figs. 51-54 Ephemeridae, p. 27 Gills slender, filamentous, and bare Leptophlebiidae, p. 81 9. Head flattened dorsoventrally, progna- thous, eyes dorsal, and labrum mostly or completely concealed under projecting anterior margin of head, figs. 360, 383- 386, 390, 394, 395 Heptageniidae, p. 151 Head hypognathous, eyes lateral, or, if prognathous, labrum completely ex- May, 1953 Burks: The Mayflies of Illinois 27 posed, figs. 199, 212, 240, 247, 254, as to be approximately parallel with Cu^ „^^^' ." , , L J • L L * in the basal area. The basal costal cross- 10. Cerci unirormly clothed with short setae, . n i i i i i • figs 199 212 veins are well developed, and the stigmatic Leptophlebiidae, p. 81 crossveins usually are not anastomosed. In Cerci bearing a dense row of setae only on many ephemerids, each compound eye in the the mesal margin of each, fig 298 ^^j^, i^ jj^jj^j -^^^ ^ ^^^^ ^^^^^ ^^^^-^^ rjaetiaae, p. y / i i • i i i i i and a light-colored upper portion, but the ppjjpiyfpDTQA p facets usually are the same size in each portion of the eye. The eye of the male in The family Ephemeridae, as defined here, some species is not much larger than the corresponds to the families Ephemeridae, eye of the female. The fore tarsus in the Polymitarcidae, and Potamanthidae in the males has five segments, the basal one very classification of Ulmer (193.-?: 195), except short, figs. 23, 24. The hind tarsus in both Fig. 48. — Hexagenia bilineata, Fig. 49. — Pentagenia vitt'u/era, Fig. 50. — Ephemera simulans, that Neoephemera, included by Ulmer in the Ephemeridae, is excluded from this family and placed in a new family, Neoephemeridae. The classification of the Ephemeridae used here is identical with that of Traver ( 1935«: 240), except for her inclusion of Neoephem- era in this family. The Ephemeridae include the largest mayflies occurring in Illinois. These are the mayflies that on warm summer evenings commonly emerge in enormous numbers from our larger rivers and lakes, and cover bridges and water-front buildings. The wings of adult ephemerids have ex- tremely numerous crossveins, and, except in Tortopus and Campsurus, a band of fine, short veinlets along the outer margin of each wing, figs. 38-43, 46, 47. In the fore wing, vein Cu^ is sinuate near the base, and the posterior branch of vein M, is curved so doral aspect of head of nymph, dorsal aspect of head of nymph, dorsal aspect of head of nymph. sexes has only four clearly differentiated segments. In Tortopus, the middle and hind legs are nonfunctional and almost completely degenerated; in Eplioron the legs are re- duced somewhat and are nonfunctional. The nymphs of all ephemerids are pro- vided with mandibular tusks and a row of completely exposed, biramous gills on either side of the abdomen, figs. 2, 55, 59. These nymphs live in the sand, gravel, or silt on the bottoms of our larger streams and lakes. Although they remain almost completely buried most of the time, they can sometimes be seen swimming freely in fairly deep water near shore. They have been observed to swim with a characteristic darting and un- dulating motion at about a foot beneath the surface. The periods in which the nymphs swim freely in the water may be near the time of molting. Nymphs in an aquarium 28 Illinois N.vhral History Sirvky Hullktin Vol. 26, Art. 1 were observed to leave the sand in the bottom, swim about in the water, and, after molting, re-bury themselves in the sand. KKV K) SIBI AMll.IES Adults 1. \cins Sc and Ri of fore wing curved pos- teriorly and continued around apical anijlc of wint;; mariiinal veinlcts want- inu, tig. 44. Middle and hind legs of both male and female completely atrophied beyond trochanter, or femur, tibia, and tarsus degenerated to mere membranous flaps; male forceps un- segmented, fig. 60 , Campsurinae, p. 28 Veins Sc and Ri of fore wing straight at apexes; marginal veinlets present, figs. 38, 40, 42, 46. Middle and hind legs beyond trochanter not atrophied or de- generated to membranous vestiges; male forceps segmented, figs. 61-63, 65-67 2 2. Marginal veinlets of fore wing extremely numerous; cubital intercalary veins straight, not attached at bases to Cui, fig. 38 Ephoroninae, p. 32 Marginal veinlets of fore wing relatively few in number; cubital intercalary veins sinuate, attached at bases to Cui, figs. 42,46 3 3. First anal vein of fore wing forked near wing margin, fig. 42 Potamanthinae, p. 30 First anal vein of fore wing not forked, fig. 46 Ephemerinae, p. 35 Mature Nymphs 1. Gills lateral, fig. 55 Potamanthinae, p. 30 Gills dorsal, figs. 2, 59 2 2. Head without a frontal process Campsurinae, p. 28 Head with a frontal process, figs. 2, 59. .3 3. Mandibular tusks upcurved Ephemerinae, p. 35 Mandibular tusks downcurved Ephoroninae, p. 32 CAMPSURINAE The subfamily Campsurinae, as defined here, corresponds to the first section of the family Polymitarcidae in the classification of Ulmer (19.S.^: 197). It includes only Tor- topus and the very closely related genus (jampsiirus in the Nearctic region. To- gether, these two genera include about 50 species in South America and Central Amer- ica, but only 4 species of campsurine may- flies have been described or identified from America north of Mexico. Of these, 2 occur in Texas only, another cannot be identified at present, and the fourth is quite generally distributed in eastern North Amer- ica. The nymphs are unknown for the Nearctic species. KKV TO GENERA Adults Middle and hind legs reduced to functionless, membranous vestiges, but with all leg-parts still discernible. . . ^ 1. Tortopus Middle and hind legs completely aborted be- yond the trochanters. 2. Campsurus 1. TORTOPUS Needham & Murphy Tortopus Needham & Murphy (1924:23). In the adults, the fore wing has veins C and Sc recurved around the apical angle of the wing, fig. 44; the veinlets along the apical wing margin are absent, vein M is forked at the wing base, and there are two long, cubital intercalary veins. The fore leg in the males is developed normally, but the middle and hind legs, as well as all of the legs in the females, are reduced to small, nonfunctional semimembranous vestiges, which, however, have all leg-parts still dis- cernible. The females never molt to the imago stage, but mate and lay their eggs as subimagoes. In adults of both sexes, gill stumps are retained along the lateral mar- gins of the abdomen. The median caudal filament is vestigial in the males, but is well developed in the females. It has, unfortunately, not been possible as yet to find the nymphs of Tortopus in Illinois. The nymphs are presumed to be burrowing forms, relatively close in struc- ture to the nymphs of (jompsurus. Charac- teristics for the latter have been given by Needam & Murphy (1924:13) and Ulmer (1920^:17). Tortopus primus (McDunnough) Campsurus primus McDunnough (1924a: 7). Campsurus incertus Traver (1935^:286). Campsurus man'ttobensis Ide (1941:155). As has been pointed out before (McDun- nough 1926:185; Traver 1935^:288), this species may be a synonym of Palingeuia puella Pictet (1843:145). The type of puella has not, so far as is known, been located and compared with recently col- lected material. Pictet's description was apparently drawn from a single mutilated May, 1953 Burks: The Mayflies of Illinois 29 female specimen, almost certainly a sub- imago. The species pitella can probably never be identified with certainty. For the present, the name primus may be used for the species. Male.—Length of body 10-14 mm., of fore wing 9-12 mm. Body of living specimen snow-white, with wings white and costal margin of each fore wing faintly shaded with bluish gray. Antennae and apical tarsal segments of each fore leg shaded with bluish gray. Fore leg with femur and tibia approxi- mately equal in length, first tarsal segment one-third as long as tibia, second to fifth tar- sal segments equal in length, each twice as long as first segment; longer of two tarsal claws as long as fifth tarsal segment, shorter claw two-thirds as long as longer one. Middle and hind legs greatly reduced, but all parts still represented by small, membranous vestiges. Genitalia, fig. 60, with two charac- teristically broad, flat penis lobes. Female.—Length of body 13-17 mm., of fore wing 16-22 mm. Body of living speci- mens snow-white, but often with a faint, longitudinal band of grayish brown on meson of pronotum and on dorsum of ab- 52 A Fig. 51/4. — Hexagenia limhata, gill of first abdominal segment. Fig. 51B. — Hextujenia limbata, gill of fourth abdominal segment. Fig. 51C — Hcxagmia limbata, gill of seventh abdominal segment. Fig. 52/4. — Ephoron leiikon, gill of first abdominal segment. Fig. 52B.—Ephoron leukon, gill of fourth abdominal segment. Fig. 52C — Ephoron Iriikon, gill of seventh abdominal segment. Fig. 53/1. — Potamanthus myops, gill of first abdominal segment. Fig. 53fi. — Potamanthus myops, gill of fourth abdominal segment. Fig. 53C — Potamanthus myops, gill of seventh abdominal segment. Fig. 54/1. — Pentagrnia vittigera, gill of first abdominal segment. Fig. SAB.—Pentagrnia -vittigera, gill of fourth abdominal segment. Fig. 54C. — Prntagenia vittigera, gill of seventh abdominal segment. 30 lii.iNois Natirai, History Sirvey Bulletin Vol. 26, Art. 1 domrn. Mcsoscutum of thorax with three loncituilinal, obscure, brown lines which converge toward scutellum. Dorsal meson of metathorax vaniu-ly stainrd with grayish ' v' 'P nif'/Si'iVl ^ Fig. 55. — Potamnttllius sp., mature nymph, dorsal aspect. brown. All legs greatly reduced, semi- membranous, nonfunctional. Known from Alabama, Arkansas, Geor- gia, Illinois, Kansas, Manitoba, Missouri, Nebraska, Ontario, and Tennessee. De- velops in large, slow rivers. Illinois Records. — Alton: Aug. 29, 1913, 29. Bloo.mington: C. C. Adams, 10 9. Champaign: Sept. 21, 1892, C. A. Hart. 19. Elizabethtown : at light, July 14, 1948, Mills & Ross, 19. Grand Tower: Aug. 14, 1898, C. A. Hart, 73 i . Havana: Aug. 10, 1889, C. A. Hart, 1 9 ; White Oak Creek, Aug. 14, 1896, C. A. Hart, 39. Momence: Aug. 16, 1938. Ross & Burks, 19. Oquawka: Sept. 26, 1947. H. H. Ross, 30 9 . QuiNcv: Aug. 10, 1889, C. A. Hart, 19. Shawneetown: Oct. 3, 1942, Krison & Ross, 19. Urbana: at light. Aug. 23, 1943, H. B. Petty, 5 9 ; Sept. 20, 1909, 2 9 . 2. CAMPSURUS Eaton Campsurus Eaton (1868:83). The adults of Campsurus differ from those of Tortopus mainly in the structure of the legs; the middle and hind legs in both sexes in Campsurus are completely aborted beyond the trochanters. The difference in the wing venation between the two, de- scribed by Needham & Murphy (1924:23) when they defined the genus Tortopus, is not reliable, according to Ulmer (1942:108). Campsurus decoloratus (Hagen) (1861: 43), known from Texas and Mexico, and circumfiuus Ulmer (1942:110), described from Texas, are the only known Nearctic species. C. ptiella (Pictet) (1843:145), described from Louisiana, has been tenta- tively placed in Campsurus, but is at present unidentifiable. POTAMANTHINAE The subfamily Potamanthinae corresponds to Ulmer's family Potamanthidae (1933: 199). It has only one Nearctic genus. 3. POTAMANTHUS Pictet Potamanthus Pictet (1845:208, pi. 25). The adults are fairly large, whitish may- flies with the vertex and the dorsum of the thorax light reddish brown. The marginal intercalary veins of the wings are not net- like, fig. 42. In the fore wing, the basal part of vein Mg is more strongly curved to the rear than is vein Cuj, fig. 42, and the first anal vein is forked near the wing margin. In the hind wing, the costal pro- jection is acute and veins M^ and Mg diverge near the wing base. The middle and hind legs of the adults are functional. The inale genitalia, fig. 61, have the penis lobes broad, flattened, and almost com- May, 1953 Burks: The Mayflies of Illinois 31 pletely fused on the meson ; each arm of the forceps has three segments. The nymphs, fig. 55, are sprawlers, with the gills extended laterally. The median caudal filament is well developed in the nymphs and in the adults of both sexes. Adult specimens of Potamanthus should be studied when freshly killed, as the faint myops. In the Museum of Comparative Zoology there is a specimen labeled as the type of myops, but it was collected a year after the description was published and cannot, therefore, be the type. It is, how- ever, a specimen determined as myops by Walsh himself, and is in agreement with the present-day concept of the species. Fig. 56. — Potamant/ius verticis, dorsal aspect of head of adult male. Fi^. 57. — Potamanthus myops, dorsal aspect of head of adult male. Fig. 58. — Potamanthus distinctus, dorsal aspect of head of adult male. color markings fade rapidly after death. Male.—Length of body 10-13 mm., of This fading occurs much more rapidly in fore wing 1 1-14 mm. Compound eyes small, alcoholic than in dried specimens. fig. 57; wings completely hyaline, with no Reliable specific characters for the nymphs crossveins black; abdomen without lateral, of this genus have not been found. salmon-pink spots or stripes, or, rarely, with small, faint, lateral spots discernible in KEY TO SPECIES living specimens; caudal filaments with ar- ticulations usually slightly darkened with Adults . . . . . red-brown or pmk. 1. Abdomen usually entirely unmarked, i?^..^ t ..uiujiii? l ,1 \, UA \ I r EMALE.—Length of body 11-13 mm., of occasionally each abdominal segment ^ •' ' with a faint, minute, pink spot on^either fore wing 12-14 mm. Eyes same size as m side; crossveins in fore wing hyaline in male; wings with no crossveins black; ab- each sex; compound eyes of male small, domen without lateral, salmon-pink spots or fig. 57 1, myops . j i ri . vu .• i . Abdomen with large, well-marked, lateral, ^^"P^^: '^^"^^l filaments wi h articulations salmon-pink spots or stripes 2 usually slightly darkened with red-brown or 2. Abdomen with lateral stripes; fore wing pink. in each sex with black crossveins; com- Known from Illinois, Indiana, Iowa, Kan- pound eyes or male moderate in size, t»,t- l- j wt- • t-> i ^ ^g 3_ distinctus ^^''' Michigan, and Wisconsin. Uevelops in Abdomen with lateral spots 3 large and moderate-sized rivers. 3. P^male with crossveins of each fore wing Illinois Records.—Adult specimens, col- black, male with those crossveins hy- 1^^.^^^ j^^e ^ ^^ August 17, are from Aurora aline, or with onlv a rew or the anterior ,^ * . s r^^ • t-\- /n i crossveins black'; compound eyes of (Fox River), Champaign, Dixon (Rock male large, fig. 56 2. verticis River), East Dubuque (Mississippi River), Both male and female with all crossveins Effingham, Freeport, Galesburg, Homer, of each fore wing black; compound eyes Kankakee, Monmouth, Monticello, Muncie, ot male small, as in hg. 57 „ „ t> \ i a -o \ 4. neglectus Oakwood, Oregon, Feoria, Kockford, Rock Island, Rockton, Sterling, and Urbana. 1. Potamanthus myops (Walsh) Ephemera myops Walsh (1863:207). Potamanthus medius Banks (1908:259). A study of the type of medius leaves no doubt in my mind that it represents the same species as the one we have been calling 2. Potamanthus verticis (Say) Baetis verticis Say (1839:42). Ephemera flaveola Walsh (1862:377). The type of Say's species is lost, but both male and female types of Walsh's species 32 Ilmnois Natural History Survey Bulletin Vol. 26, Art. 1 are in the Museum of Comparative Zo- olo^. By common consent, the identity of this species has lonji been based on the characters of Walsh's species, although Say's name has priority. There is at present no reason for changing this practice, as is mentioned below under negltctus. Male.—Length of body 7-9 mm., of fore wing 8-10 mm. Compound eyes large, fig. 56; wings with all crossveins hyaline or, in occasional specimens, with a few anterior crossveins of each fore wing darkened ; ab- domen with a row of salmon-pink spots on either side; cerci and median caudal fila- ment with articulations darkened. Kemale.—Length of body 8-10 mm., of fore wing 9-11 mm. Compound eyes small, each less than half the size of eye of male; wings with crossveins darkened; abdomen with a row of salmon-pink spots on either side; cerci and median caudal filament with articulations darkened. Known from the midwestern and north- eastern states. Develops in large and mod- erate-sized rivers. Illinois Records.—Adult specimens, col- lected May 2 to August 16, are from An- tioch, Aurora, Bloomington, Champaign, Dixon (Rock River), Foster (Mississippi River), Hardin (Illinois River), Kankakee, Keithsburg, Mount Carmel, Oregon, Proph- etstown (Rock River), Quincy, Rockford, Rock Island, Rockton, Savanna (Mississippi River), South Beloit, Sterling, Warsaw (Mississippi River), Wilmington, Yorkville. 3. Potamanthus distinctus Traver Potamanthus distinctus Traver (1935a: 280). The crossveins of the fore and hind wings are black in both sexes; the fore wing is 11 mm. long; there is a reddish-tan stripe on the vertex, pronotum, and the anterior part of the mcsonotum ; the abdomen has a salmon-pink stripe on either side; and the articulations of the cerci and the median caudal filament are darkened. The com- pound eyes of the male are moderately large, fig. 58. Known from New York and Ohio. 4. Potamanthus neglectus Traver Potamanthus neglectus Traver (193Sa:282). In describing this species, Traver men- tioned that it might eventually prove to be a synonym of verticis. IMiere is, however, nothing in the original description of Say's species that would conclusively decide the matter; if neglectus were to be placed as a synonym of verticis, it would then be neces- sary to resurrect from synonymy the name flaveola for that species at present being called verticis. I prefer to follow McDun- nough (1926:186) in considering y?flt'<'o/a a synonym of verticis, as there is no strong reason for not doing so, and the present known distribution of the species involved is in agreement with that practice. P. verticis was described from Indiana, and flaveola was described from Illinois; the species now- going under the name verticis occurs in the midwestern and northeastern states. P. neglectus is known only from the Atlantic Seaboard. The crossveins in the wings in both sexes arc darkened; the length of the fore wing of the male is 8-9 mm.; there is a reddish- brown median stripe on the vertex of the head, on the pronotum, and on the mesono- tum ; the abdomen has a row of salmon-pink spots on either side; the caudal filaments have the articulations darkened; the com- pound eyes of the male are small, as in myops, fig. 57. Known from Maryland, New York, and Pennsylvania. EPHORONINAE The subfamily Ephoroninae includes only one genus in the Neartic region, Epiioron. As used here, this subfamily corresponds to the second section of the family Poly- mitarcidae in Ulmer's classification (1933: 197). 4. EPHORON Williamson Ephoron Williamson (1802:71). Polymitarcys Eaton (1868:84). The adults of Ephoron are fairly large, snow-white mayflies with all legs of the females and the middle and hind legs of the males greatly reduced and functionless. The females do not molt to the adult stage, but mate and lay their eggs as subimagoes. The costal and subcostal areas of the fore wing are grayish purple ; otherwise the wings are snow-white. These wnngs, fig. 38, have extremely abundant crossveins and netlike marginal intercalaries suggesting the archaic Mav. 1953 Burks: The Mayflies of Illinois 33 orthopteroid archedictyon. The cubital intercalaries of the fore wing consist of three or four long, straight veins, the pos- terior one of which is attached to the anal wing margin by a series of confused, short, and irregular veinlets. The hind wing has a blunt costal angulation. In the fore leg of the males, fig. 23, the tarsus is normally developed but the femur is quite short. In the females, the median caudal filament is well developed, while, in the males, it is reduced to a minute rudiment. The nymphs, fig. 59, have prominently toothed, downcurved mandibular tusks; the gills have short, relatively inconspicuous marginal ciliae, figs. 525^ 52C. Reliable characters for separating the females to species have not yet been found. KEY TO SPECIES Adult Males Mesonotum dark brown; apicolateral angle of each penis lobe rounded, fig. 66 1. leukon Mesonotum light yellow, shaded with tan; apicolateral angle of each penis lobe acute, fig. 67 2. album Mature Nymphs Gills on abdominal segments 2-6 with lateral tracheal branches pigmented, figs. 525, C, 59 1. leukon Gills on abdominal segments 2-6 with lateral tracheal branches hyaline 2. album 1. Ephoron leukon Williamson Eplwron leukon Williamson (1802:71). Polymitarcys alius of authors, misidentification. Rearing work and field observations carried on here in Illinois show that the mature nymphs of this species, when ready to transform, migrate to the shores of the large rivers in which they develop. At dusk, they congregate in the shallow water or even in the wet mud at the edge of the water. The subimagoes emerge there, leav- ing their cast nymphal skins floating on the shallow water or partly submerged in the mud. These subimagoes take flight at once, and the males molt to the adult stage almost immediately. Molting occurs in the air, during flight, as the legs are nonfunctional. The adults then disperse to mate and lay their eggs. All the adults that emerge during one evening are, apparently, dead by the following morning. The length of adult life I observed for this species in Illinois was about one hour. My observations do not agree with those of Howard (Needham 1905:60; 1920:285), also made in Illinois. However, Howard's observations were made on a mixture of individuals belonging to the genera Ephoron and Potamanthus. My ob- servations on leukon agree closely with those made by Ide (1937^:25) on this species in Ontario. ]\Iale.—Length of body 12-14 mm., of fore wing 11-13 mm. Vertex of head light yellow, shaded with very dark gray between ocelli; anterodorsal area of mesonotum dark brown, metanotum a lighter brown ; legs light yellowish to snow-white (in freshly killed specimens), with each fore femur and tibia stained with purplish gray; abdomen white, with variable areas of gray shading Fig. 59. — Ephoron leukon, mature nymph, dorsal aspect. Small figure at left represents enlargement of fore leg to show detail. 34 Ii.i.tNois N Ml KM. History Survey Bum.etin Vol. 26, Art. 1 on apical tfrgites; ponis lobes, fi^- 66. with lateral annl<"s relatively blunt, slightly down- curved; each cercus stained with pray- lavender near base, color paling to snow- white toward apex. The nvmph. fiji. 59, was described by Ide (19-?5fl:113). Known from central, eastern, and north- eastern states and southeastern Canada. Most of the older published records of album Fi^. 60.— Torlnpus primus, male genitalia. Fi)i. 61. — Pntamantlius myops, male genitalia. Fij{. 62. — Pentagenia vittigrra, male genitalia. Fifi. 63. — Ephemera simulans, male genitalia. Fig. 67. — Epiioron album, male genitalia. Fig. 64, — Pentagenia /,^,„^r« (/^fo;v/ Walsh ( 1862: 376). halfway across the wing. The median . . . . ,n n l J I 1-1 » • u », <.„^«^ ;o no L,«,r ic Male.—Length of body K)-1J mm., ot caudal filament in both sexes is as long -is . , , , , ^m i i L Tk ^«,^- „„J *k» r,,/.,i;.i,i fore wing Il-1.< mm. 1 norax mostly dark each cercus. I he cerci and the median ^ , . , n i- i 1 , £, ^ »_ ^„i„ i„„rr »..,»i red-brown, with relatively small, light tan caudal filament are extremely long—each • • . . more than twice as long as the body. f ^'"^^ "" pro- and mesopleuron ; each ore In the nymphs, the frontal process of the ^^K dark red-brown, middle and hind legs head has a conspicuous, sharply projecting ^an to yellow; fore wmg and hind wing, f^gs. angle at each lateral margin, fig. 50. The "^6, 47, each with dark brown spots in discal mandibular tusks are long, slender, and 'irea. Abdomen yellow to tan, with dark smooth, with a few small, toothlike rasps red-brown markings: each tergite with a on the outer. side near the base. The apex P^i"- "^ l^'^eral dark blotches; each of apical of the labial palp is broad and truncate. three tergites with a pair of submedian, longitudinal, lateral stripes; sternites with KEY TO SPECIES longitudinal, lateral stripes, and a pair of submedian, longitudinal spots on each ster- .^DULTs nite; penis lobes, fig. 63, relatively wide; 1. Abdomen creamy white, without dark ,,.j^^.ji fil^^^ents dark yellow-brown, with markings 1. guttulata ,• i,- i r .' Abdomen yellowish or tan, with longi- articulations darkened. tudinal, dark brown markings 2 f EMALE.—Length of body 11-13 mm., 2. Hind wing with small, dark clouds sur- of fore wing 12-14 mm. Color pattern same rounding discal crossveins, making wing ^^ j^ ^^^ ^^^ ^^^^ ^^^^^ ^^j relative- appear spotted; genitalia with penis , , • i i- i n lobes relatively broad, fig. 63 'y '^ss extensive; legs light tan or yellow, 2. simulans fore legs shaded with light red-brown; Hind wing not spotted, discal crossveins caudal filaments light yellow, with brown not surrounded by dark clouds; gem- articulations, talia with penis lobes relatively narrow, flg 65 '3^ varia Known from the northeastern and central states and eastern Canada. This is one of Mature Nymphs ^l ^ a- • ^u r^u-the commonest maynies in the Chicago 1. Abdomen without color markings on j^^ j^ emerges along the lake front in venter 1. guttulata ^ . 0-1 Abdomen with longitudinal color markings enormous numbers every summer. The on venter 2 nymph is found near the shores of lakes 2. Hind wingpad with dark color pattern having considerable wave action and in indicated 2. simulans 1 .. • j • j 1 u- . • J -.k » • J- .• f 1 moderate-sized rivers and creeks.Hind wingpad without indication of color .,,. . „ ^ r^ r ^ -., pattern... 3, varia lllmois Kecords. — Cedar Lake: Oct. 21, 1882, 3 nymphs. Chicago: July 31, 1887, 1. Ephemera guttulata Pictet C. A. Hart, 3$ , 3 9 ; July, 1916, 1 S ; July 8, 1937, Prison & Ross, 43$, 18$. Ephemera guttulata Pictet (1843:135). "Eddyville: Lusk Creek, May 16, 1947, The wings appear to be almost solid B. D. Burks, 1$. Evanston: July 17, brown because of the dense, dark red-brown 1938, G. T. Riegel, 2 $ ; July 9, 1939, G. T. pigmentation around and between the cross- Riegel, 1 $ ; July 22, 1942, J. S. Ayars, 2 $ . veins; abdomen uniformly pale cream, with- Homer: June 30, 1925, T. H. Frison, 1 $ ; out a darker color pattern, contrasting June 10, 1926, T. H. Frison, 9 9 ; June 30, markedly with the very dark wings; cerci 1927, Frison & Glasgow, 9$, 11 9 ; Oct. 3, and median caudal filament tan to brown, 1946, L. J. Stannard, 2 nymphs. Kanka- wMth articulations very dark brown. Dis- kee: June 12, 1931, Frison & Mohr, 2$, tinctive genitalia of male figured by Need- 3 9 ; June 5, 1932, Frison & Mohr, 2 $ ; ham (1921, pi. 81, fig. 58) and others. May 31, 1938, Burks & Mohr, 3$, 19 ; May, 1953 Burks: The Mayflies of Illinois 37 June 15, 1938, Ross & Burks, 1$. Mc- Henry: June 3, 1943, Ross & Sanderson, 12. Muncie: June 29, 1919, \S ; May 25, 1941, Ivabel Johnson, 1$. Oakwood: June 6, 1925, T. H. Prison, 18 . talia. Fit genita Fijf. Fi(i PUNCTATA ^l.—Brachyfrrcus lacustr'ts, fore wing. 98.— Triiorythndes atrattts, fore wing. 99.— Tr'uorythndrs prridius, male geni- 100. — Triioryl/iodes atratus, male geni- 101.— Tricnrylhndfs slytj'uitus, male iia. 102. — Caenis jofosa, penis lobes. . U)i.—Caenis forcipata, penis lobes. Fi^. IfSA.—Catnis g'lgas, penis lobes. Fi^. 105. — Caenis amira, penis lobes. Fi^. 106. — Caenis simnlans, penis lobes. Fijs. 107. — Caenis anccps, penis lobes. Fi^. 108.— r.'rtrn/j laiipennis, male genitalia. (.After McDunnough.) Fi^. 109. — Caenis liilaris, penis lobes. Fig. 110. — Caenis punctata, penis lobes. Fig. 111. — Caenis ridens, penis lobes. Fig. 112. — Caenis diminuta, penis lobes. May, 1953 Burks: The Mayflies of Illinois 47 pellicle during flight; it is quite possible that all species of the genus do likewise. The first-described Nearctic species in this genus, allectus (Xeedham) (1905:47), is now virtually unidentifiable. It cannot be placed from the characters given in the original description alone. The types are, furthermore, either lost, or represented by only a few fragments. These fragments of specimens are not certainly the types, but might be; in any event, they are not in good enough condition to serve as a basis for an identification of the species. Reliable characteristics for the separation to species of females and nymphs of this genus have not yet been found. KEY TO SPECIES Adult Males 1. Wings with all crossveins hyaline; an- tennal scape black 1. stygiatus Wings with anterior crossveins brown; antennal scape white or yellow, tinged with red-brown 2 2. Vertex of head black 2. atratus Vertex of head mosth' light yellow 3. peridius 1. Tricorythodes stygiatiis McDunnough Tricorythodcs stygiatus McDunnough (1931<':267). Male.—Length of body 2.5-3.0 mm., of fore wing 3.5-4.0 mm. Head black, com- pound eyes and ocelli black ; each antennal scape black, pedicel tan, flagellum yellow. Pronotum black, mesonotum very dark brown, metanotum yellow-brown; meso- and metapleura dark red-brown, with vague, black markings near wing bases; thoracic sternum dark red-brown; all coxae black; femora black, with red shading and with vague, longitudinal, yellow streaks; tibiae white, mottled with black and red- brown over basal three-fourths; tarsi white or gray; wings hyaline, anterior longitudinal veins brown. Abdominal tergum black ; tergites 3-7 lighter near lateral margins: sternites dull yellow, suffused with gray, and with a median, black mark at posterior margin of each sternite; caudal filaments white, shaded with gray near bases. Geni- talia, fig. 101, yellow to white, with penis lobes relatively narrow and median inden- tation at posterior margin of forceps base relatively narrow and shallow. Known from Illinois, Michigan, New Brunswick, and Quebec. Develops in almost stagnant eddies along large streams. Illinois Record.—Wilmington: at light, Aug. 6, 1947, Burks & Sanderson, A$. 2. Tricorythodes atratus (McDunnough) Tricorythus atrata McDunnough (1923:39). It is quite possible, as McDunnough (1931^:265) has said, that atratus is the same as allectus (Needham 1905:47), al- though the characters given in the original descriptions are not quite identical. As was remarked above, the specimens at present taken for the types of allectus are not in good enough condition to serve as a basis for an identification of the species. It is preferable at present to use atratus for the species, as that name is based on a detailed description, and the types are well preserved and available for study. Male.—Length of body 3.0-3.5 mm., of fore wing 3.5-4.5 mm. Head black, com- pound eyes black, each antenna yellow or white, with faint, gray shading at base of pedicel. Pronotum black, becoming brown at lateral margins; mesonotum and metano- tum dark brown, pleura lighter brown, sternum dark brown ; coxae and trochanters dark gray ; femora gray, with black shading, subapical area of each with red-brown shad- ing; fore tibia brown, with median, black shading, middle and hind tibiae white, with black shading in middle, fore tarsus gray ; middle and hind tarsi white; wings hyaline, veins Sc and R^ shaded with gray, anterior veins and crossveins brown. Abdomen yel- low-gray or white ; tergites 1 and 2 com- pletely shaded with black, tergites 3-7 black only on meson and at posterolateral angles, apical tergites covered by black shading; sternites yellowish gray, with a median, black mark at posterior margin of each sternite; caudal filaments white, shaded with gray near bases. Genitalia, fig. 100, white or light yellow, with penis lobes relatively wide and apical, median excavation of for- ceps base relatively wide and deep. Known from Illinois, Michigan, and Quebec. Develops in almost stagnant eddies of larger streams. Illinois Records.—Mil.an: Rock River, June 4, 1940, Mohr & Burks, 1 , 91D. The three caudal filaments are relatively stout, with a whorl of three to five setae at each artic- ulation. I have observed the subimagocs of sitiiu- lans to shed the subimaginal exuviae during Fi^. 114. — Carnis simulans, mature nymph, dorsal aspect. May, 1953 Burks: The Mayflies of Illinois 51 flight, almost immediately after emerging from the nymphs. Most adult specimens of Cacnis intended for study should be killed with cyanide and mounted dry on pins or points; a few speci- mens of a series may also profitably be preserved in alcohol for ease in studying the genitalia. The colors of the specimens in alcohol fade seriously, but the characters of the male genitalia can be seen plainly in uncleared specimens preserved in alcohol. The male genitalia of dry specimens can be cleared in KOH for study, but the clearing technique is difficult. Specimens of Caenis are both small and fragile, which makes them difficult to handle without breakage during staining and clearing operations. A revision, based on adult specimens of this difficult genus, was made by McDun- nough (193 If) ; all subsequent North Amer- ican workers have leaned heavily on his work. Specific characteristics for females and nymphs of Caenis have not been found. KEY TO SPECIES Adult Males 1. Vertex of head entirely and uniformly shaded with dark gray 2 Vertex of head partly or completely white or pale yellow 5 2. Hind femur freckled with numerous, mi- nute, black dots 1. punctata Hind femur without numerous, minute, black dots; white, with an apicodorsal black spot or subapical black band. .3 3. Apex of hind femur completely encircled by a black band 2. diminuta Apex of hind femur with only a dorsal black spot 4 4. Genital forceps short and stout, fig. 105; body and fore wing each only 2 mm. long 3. arnica Genital forceps moderately long and curved, fig. 106; body and fore wing each 3.5-4.0 mm. long. . . .4. simulans 5. Abdomen lacking spiracular dots or streaks 6 Abdomen with spiracular dots or streaks .7 6. Mesonotum light red-brown; genital for- ceps short, fig. 107, apexes straight; vertex of head almost entirely white, shaded with purplish gray only at margins and near ocelli. . . .5. anceps Mesonotum light yellow; genital forceps moderately long, fig. Ill, apexes hooked; vertex of head heavily shaded with purplish gray near ocelli, light only in center 6. ridens 7. Abdominal segments 7-9 only with gray- brown spiracular streaks; segments 1-6 without spiracular dots or spots 7. hilaris Abdominal segments 1-6 with spiracular dots or spots 8 8. Vertex of head almost entirely white, with purplish-gray shading present only at anterior and posterior margins and occasionally near lateral ocelli; length of body 2 mm 8. gigas Vertex of head dark gray-purple in entire anterior two-thirds, posterior third light yellow or white; length of body 3 mm. or more 9 9. Length of body 3 mm.; genital forceps of relatively moderate length and stout, fig- 102 9. jocosa Length of body 4 mm.; genital forceps relatively long and slender, fig. 103.. 10. forcipata 1. Caenis punctata McDunnough Caenis punctata McDunnough (1931^:259). Male.—Length of body and of fore wing 3 mm. Vertex of head completely covered with purplish gray; mesonotum yellow- brown; fore femur with dark purplish-gray shading in middle and near ape.x ; middle and hind femora peppered with minute, black dots, each also with a dark gray band near apex; abdomen pale yellow, almost white, with extensive gray shading on tergites; spi- racular marks present on all abdominal seg- ments; each sternite with a pair of black, lateral dashes, sternites 1-6 each with a pair of sublateral, black dots, and sternites 7-9 each with two pairs of sublateral, black dots; genital forceps, fig. 110, short and stout. Known from New York, Ontario, Quebec, and Wisconsin. 2. Caenis diminuta Walker Caenis diminuta Walker (1853:584). Male.—Length of body and of fore wing 3 mm. Vertex of head slightly but uniformly shaded with gray; mesonotum dark chest- nut brown; fore femur shaded with gray and with a darker, transverse band near apex; fore tibia uniformly shaded with faint gray; middle and hind femora white, with a black band encircling each near apex ; abdomen white, with extensive gray shading on tergites 1-6; spiracular dots present on segments 1-8 or -9 ; sternites 2-6 each with a pair of slender, lateral, black lines; two pairs of minute dots sometimes present on each abdominal sternite, those on sternites 7-9 always darker than anterior ones; gen- ital forceps, fig. 112, short, stout, and mark- edly divergent. Known from Florida, Georgia, Ontario. 52 Illinois Natural History Survey Bulletin \'oI. 26. Art. 1 3. Cat'tiis arnica Haj:en Caenis amita Hagrn (1861:55). Male.—Length of body and of fore win^; 2.0 mm. Vertex of head completely covered by dark jiT'IV shading; mesonotum yellow- brown; fore femur extensively shaded witli dark (iray, middle and hind femora each with a black, siibapical, dorsal spot; ab- dominal termites lijjhtly shaded with jzray, and spiracular dots present on abdominal segments 1-7 or -8; genital forceps, fig. 105, short and relatively slender. Known from Maine, Maryland, Missouri, North Carolina, New York, and West \'irninia. 4. Caenis sitnulatis McDunnough Caenis simulans McDunnough (1931^:263). This is by far the commonest Illinois species of Caenis. Male.—Length of body and of fore wing J.5-4.0 mm. Head below antennae yellow, vertex completely covered with dark pur- plish-gray shading; antennae yellow. Pro- notum light yellow, with dark purple-gray shading at margins and on dorsal meson; each fore coxa shaded with grayish brown, fore femur gray, with a black apicodorsal spot, fore tibia and tarsus light gray; meso- and metanotum chestnut brown, darker brown shading present on median dorsal suture or mesoscutum, just dorsad of wing bases, and at posterior ends of outer parap- sides; apex of mesoscutum shaded with gray; gray shading present near either lateral margin of metanotum; each pleuron chest- nut brown, with dark gray shading around coxal cavities and light gray shading over prealar bridge; middle and hind legs white, with a black streak on outer side of each trochanter, and on dorsal side of each femur at base and near apex. Abdomen white or faintly stained with yellow, ter- gites 1-6 heavily shaded with dark gray, tergites 7-9 with gray shading in basolateral areas; black stigmatic dots or spots usually present on abdominal segments 1-9, these markings sometimes obsolete on segments 8 and 9; each sternite typically with a black spot near either lateral margin and another black spot on meson, in addition to a pair of minute, sublateral, black dots on each of sternites 1-7 and a pair of sublateral, black dots on each of sternites 8-10; genital forceps, fig. 106, long and slightly bowed. Female.—Length of body and of fore wing 4.0-5.5 mm. Coloration almost identical with that of male except that fore femur is light yellow, without gray shading, but with apicodorsal spots preserved; fore tibia and tarsus light yellow rather than gray, and median, black spots of abdominal ster- nites wanting or only faintly indicated. Known from the northern states and Canada. Develops in nearly or quite stag- nant water; it evidently tolerates consider- able pollution. Illinois Records.—Specimens, collected ALiy ?i to August 19, are from Antioch, Banner, Reach, Chester, Fox Lake, CjoI- conda, Havana, Herod, Kankakee, Mo- mence, Oakwood, Palos Park, Prophets- town, Richmond, Rosecrans, Serena, Spring Grove, Sterling, Wadsworth, and Zion. 5. Caenis anceps Traver Caenis anceps Traver (193Sfl:645). Male.—Length of body and of fore wing 2 mm. Vertex of head mostly white, with anterior and posterior margins edged with gray-purple, and w^ith gray-purple shading near lateral ocelli; mesonotum light red- brown; fore femur shaded with gray at apex, and fore tibia shaded with gray at base ; middle and hind femora white, with a minute, black, dorsal dot near apex of each; abdomen entirely white, without mark- ings of any kind; genital forceps, fig. 107, short and straight. Known from Missouri and New York. 6. Caenis ridens McDunnough Caenis ridens McDunnough (1931^:256). Male.—Length of body and of fore wing 2 mm. Head white, vertex lightly shaded with gray-purple, this shading darker near lateral and anterior ocelli, median area of vertex relatively pale; antennae white. Pro- notum white, with minute, purplish gray- shaded area at each anterolateral angle; gray-purple shading present around each fore coxal cavity and on fore coxa; fore leg white, fore femur faintly shaded with gray at apex, fore tibia gray; meso- and metano- tum pale yellow, with light purplish brown shading on median, longitudinal line of meso- scutum and on apex of mesoscutellum ; pleuron light yellow, with purplish brown shading around coxal cavities; all thoracic .Mav, 1953 Burks: The Mayflies of Illinois 53 sternites white ; middle and hind legs en- tirely white. Abdomen white, without spi- racular spots or streaks; genital forceps, fig. Ill, stout and moderately long. Fem.ale.—Length of body and of fore wing 2.5-3.0 mm. Head almost entirely white, with faint gray shading extending across middle of vertex only; fore femur with gray shading at apicodorsal angle ; ab- dominal tergites 1 and 2 each with a pair of sublateral, transverse dark spots. Known from Illinois, Kansas, Michigan, Ontario, and Wisconsin. Develops appar- ently in eddies in small rivers. Illinois Records. — Auror.a: at light, July 17, 1927, Prison & Glasgow, 22 c5 , 4 9 . Lake Forest: J. G. Needham, 1 $ (Traver 1935fl:653). Oakwood: at light, July 10, 1927, Prison & Glasgow, 53 ^ , 21 9 . 7. Caenis hilaris (Say) Ephemera hilaris Say (1839:43). Male.—Length of body and of fore wing 2.0-2.5 mm. Head white, faint lavender shading present on vertex near lateral ocelli; antennae white. Pronotum white, with faint gray-brown shading at each an- terolateral angle; a fairly large, gray-brown spot present on outer side of each fore coxa; fore leg white, with gray shading at apex of femur; meso- and metanotum light yellow, with a prominent, gray-brown spot near apex of mesoscutellum, this spot often ex- tending forward onto mesoscutum; meso- and metapleura white, with vague gray- brown shading around coxal cavities; all thoracic sternites white; middle and hind legs white, with a black spot on dorsal side near apex of each femur. Abdomen white, with gray shading on first tergite and prom- inent, gray-brown spiracular lines on tergites 7-9; genital forceps, fig. 109, short and stout. Female.—Length of body and of fore wing each 2.5-3.0 mm. Coloration identical with that of male except that vertex of head is slightly darker, each fore femur has a dorsoapical, black spot, and spiracular lines may be present on tergites 5 and 6 as well as on apical tergites. Known from the eastern and central states. Develops in eddies of moderate-sized and large rivers. Illinois Records. — Dixon: June 27, 1935, DeLong & Ross, Mi. Elizabeth- towx : June 22, 1932, Dozier k Park, 99. Foster: Mississippi River, July 22, 1939, B. G. Berger, 89. Fulton: July 20, 1927, Prison & Glasgow, 2$. Homer: Aug. 10, 1925, T. H. Prison, 29. Jackson Island, in Mississippi River opposite Hannibal, Mo.: Sept. 6, 1940, G. T. Riegel, 1 hfmfrtUa Walsh (1862:377). Drunrlla Nccdham (1905:42). (:/iilono/>/iora Htngtssim (1908:243; 1909:6). Torlryti Lestage (1917:366). Timf>anoga Necdham (1927:108). Eatotiflla Necdham (1927:108). This nenus now includes more than 80 Nearctic species, only 1 1 of which have, so far, been taken in Illinois. Quite a few more species of Kt^lu iiuii ll5; abdominal termites lacking pale spots at bases of tubercles 18- subvaria Dorsal abdominal tubercles more re- duced, fig. 166; abdominal tcrgites hav- ing a pale spot at base of each tubercle 21. rotunda {BICOLOR CJroup; 22. Distance between rows of dorsal abdomi- nal spines suddenly increased on seg- ment 5 28. bicolor Distance between rows of dorsal abdomi- nal spines uniformly increasing trom segments 1 to 7 30. minimella 23. Distance between dorsal abdominal spines on segment 5 less than length of that segment at median line 24 Distance between dorsal abdominal spines on segment 5 equal to or greater than lenKth of that segment at median line ... 25 24. Rows of dorsal abdominal tubercles parallel, fig. 164 24. temporalis Rows of dorsal abdominal tubercles con- verging posteriorly. 22. prudentalis 25. Posterolateral spine of abdominal seg- ment 3 well developed, its length twice as great as width at base 26 Posterolateral spine of abdominal segment 3 reduced, its length only as great as width at base 28 26. Posterolateral spine of abdominal segment 9 slightly incurved; lateral margin of segment 9 almost straight 31. funeralis Posterolateral spine of abdominal segment 9 straight; lateral margin of segment 9 clearly convex 27 27. Dorsal abdominal tubercles of segments 1-3 long and slender, fig. 158 23. lutulenta Dorsal abdominal tubercles of segments 1-3 short and blunt, fig. 159 25. coxalis 28. Distance between rows of dorsal abdomi- nal spines increasing from segments 2 to 7 29. verisimilis Rows of dorsal abdominal spines almost parallel 32. aestiva 29. Paired dorsal tubercles present on occiput, thorax, and abdomen. .33. attenuata Dorsal tubercles wanting on occiput, thorax, and abdomen 30 30. Second and third abdominal tergites with posterolateral angles produced as spine- like projections, fig. 163 27. lita Second and third abdominal tergites with posterolateral angles not produced, fig. 1 62 26. simplex WALKERI Group 1. Ephemerella lata .Morj^an EphrmerrUa lata Morgan (1911:112). Ephemrrflla inftata McDunnough (1926:187). Male.—Length of body and of fore wing 6-7 mm. Body generally very dark brown, almost black, with abdominal tergites slightly lighter in color than thorax. Wings hyaline, with most veins and crossveins hyaline, veins near costal margin of fore wing very light yellow. Cjenitalia with penis lobes fused al- most to tips, penial spines lacking; second forceps segment short and subangulate, with a sharp median constriction, fig. 122; and 718 I7IC Fig. 167. — Ephemerella frisoiii, maxilla of mature nymph. Fig. 168. — Ephemerella needhami, maxilla of mature nymph. Fig. 169.—Ephemerella deficiens, maxilla of mature nymph. Fig. 170/1. — Ephemerella temporalis, gill of fourth abdominal segment. Fig. 170fl.—Ephemerella temporalis, gill of seventh abdominal segment. Fig. 170C — Ephemerella temporalis, gill of fifth abdominal segment. Fig. 171 A.—Ephemerella needhami, gill of third abdominal segment. Fig. 171B.—Ephemerella needhami, gill of seventh abdominal segment. Fig. 171C.—Ephemerella needhami, gill of fifth abdominal segment. -Mav. 1953 Burks: The Mayflies of Illinois 65 third forceps segment three times as long as wide. Nymph.—Head and body without dorsal spines and tubercles. Frontal shelf of head with a pair of small, triangular projections, fig. 156. Fore fem.ur enlarged and toothed on anterior margin. Known from Maine, Michigan, New York, North Carolina, and Quebec. 2. Ephemerella tuherctilata Morgan Ephemerella tuheiculata Morgan (1911:112). Male.—Length of body and of fore wing 8-9 mm. Body generally very dark red- brown, with middle abdominal tergites usually yellow-brown. Wings hyaline, veins slightly grayish or gray-brown. Genitalia with penis lobes fused almost to tips, penial spines lacking, and inner angles of peritreme acute, fig. 118; second forceps segment evenly bowed from base to apex, a slight inner en- largement near base; third forceps segment four times as long as wide. Nymph. — Head with frontal shelf notched below bases of antennae, and with a pair of horns on vertex. Each fore femur enlarged and toothed on anterior margin. Thorax and abdomen with dorsal, paired tubercles. Known from Maryland, New "^'ork, North Carolina, Ontario, Quebec, and Ten- nessee. 3. Ephemerella walkeri Eaton Bactis fuscata Walker (1853:570). Name preoccupied. Epiiemerella nxalkeri Eaton (1884:129). New name. Ephemerella bispina Needham (1905:43). Ephemerella fuscata (Walker). McDunnough (1931t/:214) ; Traver (1935^:600). Male.—Length of body and of fore wing 7-8 mm. Body generally dark brown, with abdominal tergites slightly lighter toward lateral margins. Wings hyaline, veins slightly stained with yellow. Genitalia with penis lobes fused almost to tips, spines want- ing, and inner angles of peritreme blunt, fig. 119; second forceps segment only slightly bowed, with an inner enlargement near base; third forceps segment four times as long as wide. Nymph.—Head with a broad frontal shelf having a notch beneath each antennal base, fig. 155; vertex lacking tubercles. Each fore femur enlarged and toothed at anterior margin. Prothoracic tubercles small and represented by a single pair laterally; dorsal abdominal tubercles minute. Known from Indiana, New Brunswick, Ontario, and Quebec. 4. Ephemerella cornutella McDunnough Ephemerella cornutella McDunnough (1931^:82; 1931^:211). Male.—Length of body and of fore wing 6-7 mm. Body generally very dark brown, abdominal tergites somewhat lighter on mesal area. Wings hyaline, veins slightly tinged with faint yellow; crossveins almost invisible. Genitalia, fig. 121, with penis lobes fused almost to tips, penial spines wanting; second segment of forceps relatively short and straight, an inner enlargement near base; third segment four times as long as wide. Nymph.—Frontal shelf of head with a pair of strongly incurved, lateral horns, fig. 157. Fore femur enlarged and bearing teeth on anterior margin. Head, thorax, and ab- domen without dorsal tubercles or spines. Known from Georgia, New Brunswick, New Hampshire, New York, North Caro- lina, Nova Scotia, Quebec, and West V^ir- ginia. 5. Ephemerella cornuta Morgan Ephemerella cornuta Morgan (1911:114). This species differs from cornutella only in that the length of body and of fore wing of male are 9-10 mm. each, second forceps segment of male genitalia is relatively longer and more bowed, fig. 120, and frontal shelf of head of nymph bears a pair of horns which are relatively less incurved, fig. 154. Known from Connecticut, Maine, New Hampshire, New York, North Carolina, Pennsylvania, Quebec, and Tennessee. SERRATA Group 6. Ephemerella frisoni McDunnough Ephemerella frisoni McDunnough (1927^: 10). Male.—Length of body and of fore wing 5.0-6.5 mm. Head dark brown, eyes tan; antennal pedicel tan, flagellum brown. Thoracic notum dark brown, lateral areas, near wing bases, tan; venter dark brown; 66 Illinois Natlrai. History Survey Hui.i.iniN Vol. 26, Art. 1 "^^^^i ^•x;«te>» Fig. 172. — Epiiemerclla frisoui, mature nytnph, dorsal aspect. fore femur light brown, fore tibia and tarsus and all of middle and hind legs white; wings hyaline, with brown stain at base of each wing, each fore wing milky in stigmatic area. Abdominal tergites 1-7 and anterior half of tergite 8 white, usually with a fine, median, dorsal, brown line and a pair of small, brown, lateral marks on each tergite; pos- terior half of tergite 8. and tergites 9 and 10, light brown; abdominal sternum white, usually with a pair of lateral, brown dots on each stcrnite; caudal filaments entirely white, articulations not darkened. Genitalia, fig. 123, white, with forceps faintly shaded with tan. NvMPH.—Fig. 172. Length of body 5.0- 6.5 mm., of caudal filaments 2.5-3.5 mm. General color light yellowish tan, sometimes almost white, with small and variable brown markings. Vertex of head, dorsal area of pronotum, and (usually) basal area of front wingpads with irregular, light brown markings; apexes of femora and bases of tibiae usually shaded with light brown; a minute, dark brown dot present at apicoventral angle of each trochanter. Dorsal part of abdominal ter- gites fairly uniformly shaded with light brown in area not covered by gills, elongate, dark brown markings along line of inner dorsal margins of gills and on median dorsal line; abdominal venter rather uniformly shaded with light tan, this shading freckled with light yellow or white dots; a minute, dark brown dot present near lateral margin of each abdominal sternite, these dots form- ing a sublateral row on either side of ab- dominal venter; basal half of each postero- lateral projection of sternites shaded with tan; each caudal filament with a single tan crossband usually present near base. Head and thorax without tubercles; max- illary palps present, but somewhat degen- erated, fig. 167; each tarsal claw with six to eight denticles; posterolateral angles of abdominal segments 4—9 produced, bluntly pointed; posterior margin of second abdom- inal tergite with a pair of extremely small, submedian tubercles; tergites 3-7 with these tubercles relatively well developed ; eighth tergite with tubercles greatly reduced, but discernible, tubercles wanting on ninth ter- gite ; pairs of tubercles converging slightly from tergites 3 to 7, rudimentary tubercles more widely spaced on tergite 8; abdominal segments 1 and 2 without gills, segments 3-7 bearing platelike gills; caudal filaments with relatively few, short setae at each articula- tion, these setae not longer nor more dense in apical than in basal area of filaments. Known from Illinois and Missouri. De- velops in fairly rapid creeks or small rivers. Illinois Records. — Muncie, Stony Creek: June 8, 1927, T. H. Prison, 1 N; May 22, 1942, Ross & Burks, \$. Oak- wood, Salt Fork River: June 6, 1925, T. H. Frison, 1 $ ; June 9, 1926, Frison & Auden, i$ ; May 21, 1928, T. H. Frison, 4 N; June 29, 1929, T. H. Frison, 2 N; June 14, 1935, C. O. Mohr, 6 N; May 21, 1936, Mohr & Burks, 3 N; June 11, 1936, C. O. Mohr, 9 N; May 22, 1942, Ross & Burks, 5 N. 7. Ephemerella sordida McDunnough Epiiemerclla sordida McDunnough (1925^:42; 1931^:205). Male.—Length of body 4.5-5.0 mm., of fore wing 5-6 mm. Body very dark brown, almost black, with abdominal sternites May, 1953 Burks: The Mayflies of Illinois 67 somewhat lighter; wings hyaline, all veins only very slightly darker than membrane. Caudal filaments white throughout. Geni- talia, fig. 124: penis lobes with a pair of prominent, lateral tubercles, second forceps segment slightly bowed, and third forceps segment as broad as long. Nymph.—Head, thorax, and legs conspic- uously hairy; maxillary palp present, but reduced; fore femur not toothed on anterior margin, but bearing a few spicules ; ab- dominal tergites with a double row of sub- mesal, papillate protuberances; caudal fila- ments bearing only short spines throughout their length. Known from Ontario and Quebec. 8. Ephemerella serrata Morgan Ephemerclla serrata Morgan (1911:109). Male.—Length of body and of fore wing 5-6 mm. Thorax yellow-brown, abdominal tergum red-brown, and abdominal venter yellow-brown, without transverse rows of black dots. Wings hyaline, tinged with brown at bases, and veins faintly shaded. Genitalia, fig. 128, with penis lobes fused almost to tips, and a lateral tubercle present on each penis lobe near tip; second forceps segment bowed toward apex; third forceps segment as broad as long. Nymph.—Vertex of head roughened, but without distinct tubercles. Prothorax with a pair of small, submedian, dorsal tubercles near posterior margin; each tarsal claw with three or four denticles. Abdominal tergites with a double row of submedian, wartlike tubercles; caudal filaments bearing only short setae. Known from Maryland, Massachusetts, New York, North Carolina, Quebec, and West Virginia. 9. Ephemerella serratoides McDunnough Ephemerclla serratoides McDunnough (1931A: 83; 1931^:207). Male.—Length of body and of fore wing 5-6 mm. Thorax yellow-brown, with dark brown shading; abdominal tergites red- brown, with darker brown markings; ab- dominal sternites lighter in color than ter- gites, each sternite bearing an arcuate, trans- verse row of four black dots ; wings hyaline, with veins faintly shaded. Genitalia, fig. 126, differ only slightly from those of serrata. Nymph.—Head and thorax smooth, with- out tubercles or conspicuous hairs; fore femur bearing a few spicules on posterior margin; each tarsal claw with six or seven denticles. Abdominal tergites with a double row of small, submedian, wartlike pro- tuberances; caudal filaments with only short setae. Known from IVLnryland, North Carolina, Quebec, and West Virginia. 10. Ephemerella deficieris IMorgan Ephemerclla deficieris Morgan (1911:111). Ephemerella atrcscens McDunnough (1925<::43). Male.—Length of body and of fore wing 5-6 mm. Head and body very dark brown, with abdominal sternites uniformly tan. Wings hyaline, with brown staining at wing bases; veins faintly darker than wing mem- brane. Genitalia, fig. 133: penis lobes fused only two-thirds of the way to tips, and lateral tubercles present on each penis lobe near apex ; second forceps segment is rela- tively straight. Nymph.—Head and thorax smooth, with- out tubercles; maxillary palp entirely want- ing, fig. 169; each tarsal claw with eight or nine denticles. Abdominal tergites lacking mid-dorsal tubercles; caudal filaments bear- ing only short setae. Known from Georgia, Massachusetts, Michigan, New Brunswick, New Hamp- shire, New York, North Carolina, Nova Scotia, Ontario, Quebec, and West Virginia. INVARIA Group IL Ephemerella needhami McDunnough Ephemerella excrucians Needham (1905:47), not Walsh. Misidentification. Ephemerella needhami McDunnough (1925//: 171). New name. Male.—Length of body ar.d of fore wing 6-8 mm. Head, thorax, and abdominal tergum dark red-brown to almost black; abdominal venter mostly light red-brown. Head red-brown, face below ocelli yellow; in life, each eye red-tan in upper portion, yellow in lower portion ; antennal scape yellow, pedicel and flagellum brown. Tho- rax dark red-brown to almost black, with yellow spot on sternum between each pair of coxae; fore leg sm.oky brown, middle and hind legs yellow, with vague brown shading 68 Illinois Natlrai. History Survey Bulletin Vol. 26, Art. 1 on outer sides of coxa ami near apex of femur; \vinj;s hyaline, with brown stain at bases, principal veins liyht yellow. Ab- dominal terj^um tiaric red-brown, usually with a pair of yellow, submedian spots at anterior margin of each termite, occasional specimens with a dorsal, median, lonjiitudi- nal, yellow stripe; sternites light red-brown, with transverse yellow area near anterior margin of each sternite; four minute, black marks on each sternite; genitalia, fig. 1.^1, yellow-brown, with smoky brown shading toward apexes; caudal filaments uniformly gray-brown, articulations not darkened. Female.—Length of body 7-8 mm., of fore wing 8-9 mm. Color in general lighter than in male, with dark red-brown areas of male being replaced by yellow-brown. En- tire sternum of thorax and abdomen yellow, faintly shaded with brown near apex of mesosternum; fore leg yellow, with brown shading near apex of femur; wings faintly brown at bases; caudal filaments very light yellow, basal articulations red. Nv.MPH.—Length of body 6-8 mm., of caudal filaments 3.5-4.5 mm. Color ex- tremely variable, ranging from an almost uniformly dark brown form to a form with a light yellow, or white, longitudinal, mcsal stripe that extends from vertex to tenth ab- dominal tergite; lateral margins of prono- tum and abdominal segments usually light yellow or white; caudal filaments usually with narrow, brown crossbands throughout their lengths. Head and thorax without dorsal tu- bercles; maxillary palps well developed, fig. 168; each tarsal claw with 8 to 10 denticles; each fore femur with stout, blunt spines along posterior margin and near apex, fig. 161 ; posterolateral angles of abdominal seg- ments 3-9 produced and spinelike; tergites 2-8 each with a pair of long, submedian tubercles, these forming two almost parallel rows; caudal filaments bearing long setae in apical areas. Known from Illinois, Indiana, Maine, Michigan, New York, Nova Scotia, and Quebec. Develops in cool, fairly rapid creeks or small rivers. Illinois Records. — Aroma Park, Kan- kakee River: June 11, 1947. B. D. Burks, 4^ , 3 9. Eddyville, Lusk Creek: April 4, 1946. Burks & Sanderson, 4 N; May 24. 1946, Mohr & Burks, 1 N; May 16-17! 1947, B. D. Burks, 1 6,2 9 . 1 N. Kanka- kee. Kankakee River: April 30, 1931, T. H. Frison, 45 N ; April 23, 1935, Ross & Mohr, 5 N ; Mav 17, 1935, H. H. Ross, 9 N ; July Fig. 173. — Ephetncrella argo, mature nymph, (lorsal aspect. 21, 1935, Ross & Mohr, U. Momence, Kankakee River: June 4, 1932, Frison & Mohr, 76 ; May 26, 1936, H. H. Ross, 4<5 ; May 17, 1937, Ross & Burks, 24 N; June 1. 1937, B. D. Burks, 1 ,5 ; Mav 15, i938, Ross & Burks, 8 N; May 21, 1940, Mohr li May, 1953 Burks: The Mayflies of Illinois 69 & Burks, 2 X; June 3-4. 1947. B. D. Burks, 6S, 19. 12. Ephemerella atirivillii (Bengtsson) Cliitonopfiora auri-villii Bengtsson (1908:243; 1909:8). Ephemerella aror.ii Eaton (1908:149). Ephemerella norda McDunnough ( 1924^/: 223). Ch'itonoplnra aurivilliusi Lestage (1930a: 204). Emended name. Ephemerella conciiinata Traver (1934:219). New synonymy. Male.—Length of body 10-11 mm., of fore wing 11-12 mm. Thorax red-brown, with lateral areas dark brown ; wings hya- line, with stigmatic areas milky and veins brown. Abdominal tergites with anterior third of each segment light brown and pos- terior two-thirds dark brown ; abdominal sternites yellow-brown ; caudal filaments uniformly dark brown. Genitalia, fig. 130. distinct from those of all other North Amer- ican species: penis lobes divided almost to bases, inner margins of lobes provided with numerous minute spines; second forceps seg- ment suddenly enlarged at apex. Xymph.—Head and thorax entirely lack- ing dorsal spines or tubercles; maxillary palps well developed; each fore femur bear- ing spicules at posterior margin and near dorsal apex ; each tarsal claw with 8 to 1 1 denticles; each abdominal tergite with a pair of light-colored, submesal spots at pos- terior margin, on each spot a cluster of minute spines and a small, acute tubercle; caudal filaments with long setae near apexes. Known from Alaska, Alberta, Labrador, Michigan, Montana, Ontario, Pennsylvania, Quebec, and northern Europe. This species is distributed throughout the northern part of the Holarctic region. 13. Ephemerella septentrionalis McDunnough Ephemerella septentrionalis McDunnough (1925/':171; 1931^^:201). Male.—Length of body 8-9 mm., of fore wing 10-11 mm. Dorsum of thorax and abdomen brown; venter yellow-brown; wings and wing veins hyaline. Genitalia, fig. 134, distinct from those of all other eastern North American species: slender lateral projections of penis lobe are virtually straight and directed posteriorly: mesal area of each lobe with two or three stout spines; second forceps segment relatively straight, but enlarged suddenly at apex. Nymph.—Head, thorax, and abdomen without dorsal spines or tubercles; legs conspicuously long, slender, and hairy; each tarsal claw with 10 to 12 denticles; caudal filaments bearing long setae in apical regions. Known from New York, Ontario, and Quebec. 14. Ephemerella argo Burks Ephemerella argo Burks (1949:232). Male.—Length of body 8 mm., of fore wing 9 mm. Thorax light yellowish tan, with vague brown markings ; abdomen light yellowish tan, tergites with large areas shaded with brown. Head deep cream colored, vertex with ob- scure, light gray markings; each antennal scape and pedicel cream colored, flagellum brown; eyes yellowish tan. Legs deep cream colored, apex of fore tibia and second and third fore tarsal segments darkened ; wings hyaline, stigmatic areas milky, anterior veins slightly yellow stained, other veins hyaline. Abdominal tergites light yellowish tan, with brown shading: mid-dorsal area of tergites 1-4 almost completely brown, tergites 5 and 6 shaded only near meson, tergites 7-10 completely brown, shaded on mid-dorsal area; venter of abdomen light yellowish, with vague, longitudinal, brown line near each lateral margin of each sternite; geni- talia, fig. 138, light yellowish tan; caudal filaments light yellowish tan, articulations brown. Nymph.—Length of body 7-9 mm., of caudal filaments 4—5 mm. Body principally yellowish tan, with a prominent, brown color pattern, fig. 173; caudal filan:ents each with one to three narrow, brown crossbands in middle and apical areas. Head, thorax, and abdomen without dor- sal spines or tubercles; maxillary palps well developed ; each tarsal claw with six to nine denticles; posterolateral angles of abdominal segments 3-9 produced, spinelike; caudal filaments bearing long setae in apical areas. Known from Illinois and Indiana. Prob- ably a large-river species. Illinois Record. — Mount Carmel, Wa- bash River: April 2, 1932, Prison & Ross, 2 N. 70 Illinois Natural History Survey Bulletin Vol. 26, Art. 1 15. Ephemrrfllti ora Hurks Ephemerrlla ora Burks (1949:235). Mali;.—Lt-nnth of boily 7 mm., of fore win;: 8 mm. Head and body yellow, shaded w ith tan and brown. Head yellow, shaded with tan between eyes and around ocelli; eyes pinkish tan; each antennal scape and pedicel yellow. rtai;elliim brown. Thorax yellow, with tan shading on dorsomedian area of pronotum, mesonotum mostly tan ; le^js yellow, with apex of each fore tibia and apex of each of the basal three fore tarsal segments dark- ened; win^s and veins hyaline, with an- terior two veins of fore wing stained with faint yellow. Ground color of abdomen yellow, basal tergites with mid-dorsal area of each heavily shaded with brown, apical three tergites pinkish tan; eighth sternite with posterolateral angles pink; genitalia, fig. 127, yellow; caudal filaments light yel- low, articulations black. Female.—Length of body 7.5 mm., of fore wing 9 mm. General color similar to that of male, but lighter; caudal filaments white, articulations black. Known from Illinois. Apparently a large- river species. IHinois Record. — Mount Carmel: April 22, 1946, at light, Mohr & Burks, 1 $ , 1$. 16. Ephemerella excrucians Walsh Ephcmrrella excrucians Walsh (1862:377). Ephemerella semifiaz'a McDunnough (1927/-': 300). New synonymy. McDunnough (1931^:192) long ago ex- pressed the opinion that setniftava would prove to be a synonym of excrucians. Male.—Length of body 5.5-7.5 mm., of fore wing 7-9 mm. Dorsum of thorax dark red-brown, dorsum of abdom.en varying from dark red-brown to almost black; ab- dominal venter slightly lighter in shade than dorsum. Head red-brown; eyes yellow in living insect; each antennal pedicel red-brown, flagellum smoky brown. Legs yellow, seg- ments of each fore tarsus darkened at tips. Wings hyaline, veins at costal margin of fore wing slightly yellowish ; other veins and all crossveins hyaline ; sometimes a faint red-brown staining present at bases of wings. Caudal filaments white, basal artic- ulations light red-brown. Genitalia, fig. 137, with penis lobes only slightly expanded near apexes, each lobe bearing two or three short, stout dorsal spines in basal position, and sometimes one or two lateral spines on either side; second segment of forceps straight and not expanded at apex. Nymph.— (Described from two specimens reared in Michigan by Dr. J. W. Leonard.) Length of body 5-6 mm., caudal filaments 3 mm. General color dark brown, with relatively large, pale markings; caudal fila- ments white or pale yellow, with faint, darker crossbands throughout. Head, thorax, and abdomen entirely with- out dorsal tubercles; maxillary palps present, segmented; each tarsal claw with seven or eight ventral denticles; posterolateral angles of abdominal segments 4—9 produced as small, relatively blunt spines; caudal fila- ments bearing long, dense setae in apical areas. Known from Illinois, Michigan, New Brunswick, Oklahoma, Ontario, and Que- bec. The only Illinois specimen of this species I have seen is the lectotype in the Museum of Comparative Zoology. Now known to develop in a cold, rapid river. Illinois Record. — Rock Island: \2 $ , 5 9 , B. D. Walsh (Walsh 1862:377). 17. Ephemerella dorothea Needham Ephemerella dorothea Needham (1908:190). Male.—Length of body 5-6 mm., of fore wing 7-8 mm. Head and body pale yellow, almost white. Eyes light red, antennae yellow. Thorax pale yellow, without darker shading; wings and veins hyaline; legs en- tirely yellow, with each fore tarsus faintly darkened. Abdomen entirely light yellow, without darker areas or shading; caudal filaments white, articulations not darkened. Genitalia, fig. 132, light yellow, with each penis lobe bearing six to eight stout spines in basal position ; second forceps segment enlarged at apex. Nymph.—Length of body 6-8 mm., of caudal filaments 4—5 mm. General color pale yellow-brown, with small, light tan, freckle-like spots and larger, pale markings; each caudal filament usually with two or three narrow, brow-n crossbands near tip. Head, thorax, and abdomen entirely with- out dorsal tubercles; maxillary palps well developed; each tarsal claw with six to nine denticles; posterolateral angles of ab- May, 1953 Burks: The Mayflies of Illinois 71 dominal segments 4—9 slightly produced as relatively blunt spines; caudal filaments bearing long, dense setae in apical areas. Known from Connecticut, Illinois, In- diana, Michigan, New Brunswick, New Hampshire, New York, North Carolina, Pennsylvania, Quebec, South Carolina, Ten- nessee, Vermont, Virginia, and West Vir- ginia. Develops in fairly large rivers. Illinois Records.—Golconda: May 13, 1932, Prison, Mohr, & Ross, 4 N. Mount Carmel: Wabash River, April 2, 1932, Prison & Ross, 19 N. 18. Ephemerella subvaria McDunnough Ephemerella subvaria McDunnough (1931Z':84; 1931^:194). Male.—Length of body 8-9 mm., of fore wing 9-10 mm. Head, thorax, and abdom- inal dorsum dark brown; abdominal venter light red-brown; wings hyaline, with veins and crossveins light brown. Genitalia, fig. 136, with penis lobes broad and with five or six stout, basal spines on either side; oc- casionally one or two apical, ventral spines present also; second forceps segment rela- tively straight, with apex suddenly expanded. Nymph.—Head and thorax entirely with- out dorsal spines or tubercles, but abdominal tergites with relatively well-developed, sub- median spines, fig. 165; each tarsal claw with seven to nine denticles; caudal filaments bearing long setae in apical regions. Known from Michigan, Ontario, Pennsyl- vania, Quebec, and Wisconsin. 19. Ephemerella fratercula McDunnough Ephemfrella fratercula McDunnough (1925a:213). Male.—Length of body 7 mm., of fore wing 8 mm. Thorax and dorsum of terminal abdominal segments light brown, basal ab- dominal segments dark brown on dorsum; venter yellow; wings and wing veins hyaline. Genitalia, fig. 129: each penis lobe with two or three stout, dorsal spines and seven to nine ventral ones; second forceps segment almost straight, suddenly enlarged at apex. Known from Quebec. 20. Ephemerella invaria (Walker) Baetis invaria Walker (1853:568). Male.—Length of body and of fore wing 8-9 mm. Head light red-brown, eyes reddish orange. Thorax light red-brown; pronotum red-brown, with faint gray shading; thoracic sternum dark red-brown; legs light yellow, almost white, with apex of each fore femur and fore tibia stained with red-brown; wings hyaline, longitudinal veins stained with light brown. Abdominal tergum smoky brown, becoming slightly lighter on apical tergites; sternum uniformly yellow-brown; caudal filaments white, articulations dark. Genitalia, fig. 135, light yellow; each penis lobe bearing five to eight stout, dorsal spines in basal and lateral positions on either side and, in most specimens, a single pair of ventral spines at apex, in some specimens, as many as four apical spines; second forceps segments sharply expanded at apex. Nymph.—Length of body 7-9 mm., of caudal filaments 4—5 mm. Color of body varying from dark brown with yellow mark- ings to yellow with small, brown markings; thorax of light-colored specimens usually with two brown crossbands; abdominal ter- gites 5 and 6, in area between gills, partly or almost completely light colored. Head and thorax without dorsal tu- bercles; maxillary palps well developed; each tarsal claw bearing five to seven denticles; abdominal segments 4—9 with well-developed, stout, spinelike projections at posterolateral angles, segment 3 often with rudimentary posterolateral spines; minute to obsolescent dorsal, submedian spines present on abdom- inal tergites 3-9; caudal filaments bearing long, dense setae in apical areas. Known from Illinois, Maryland, Michi- gan, New York, Ontario, Quebec, and Wis- consin. Develops in fairly rapid, moderate- sized rivers. Illinois Records.—Dixon : Rock River, May 22, 1925, D. H. Thompson, 3 N. Oregon: Rock River, May 15, 1930, Prison & Ross, 1 N. Rockford: Rock River, May 4, 1926, D. H. Thompson, 13 N. Rockton: Rock River, May 15, 1926, D. H. Thomp- son, 1 N. 21. Ephemerella rotunda Morgan Ephemerella rotunda Morgan (1911:113). Ephemerella feminina Needham (1924:309). Male.—Length of body and of fore wing 9-1 1 mm. Thorax light pinkish yellow, with brown markings; abdominal dorsum yellow, with a broad, brown crossband on each segment; venter light yellow or white 72 Ii.i.iNois Nati'rai. History Survey Rui.ketin Vol. 26, Art. 1 with, occasionally, faint tan crossbands; \vinj;s hyaline, with veins faintly yellow. Genitalia, (ij;. 145, liiffer from those of /'«- t'iiria in possessinj: a ventral, subbasal ;i;roup of two or three spines on each penis lobe. Nymph.—Dorsal tubercles on thorax and head absent, but dorsal, subniedian abdom- inal spines present, although small, i\g. 166; each tarsal claw with five to eight denticles; caudal filaments with long setae in apical regions. Known from Michigan, New \Ork, North Carolina. Ontario, Quebec, and Wisconsin. HICOLOR Group 22. Ephenierella prudentalis McDunnough Eplumfrella prudentalis McDunnough (1931rt:40). M.ALE.—Length of body and of fore wing 7-8 mm. Thorax and basal abdominal ter- gites red-brown, color gradually changing to yellow on apical tergitcs; sternites yellow, with black markings; wings hyaline, brown stain at bases; veins hyaline, occasionally tinged with tan. (Jenitalia, figs. 140, 141, dilifer from those of all other eastern North American species in having a large, ventral, subapical enlargement on each penis lobe. Nymph.—Head with a pair of small occipital tubercles; dorsum of abdominal tergites with two rows of submedian spines converging posteriorly; caudal filaments bearing long setae in apical areas. Known from Quebec. 23. Ephemerella lutulenta Clemens Eplicmerella lutulenta Clemens (1913:335). Ephemerella linrata Clemens (1913:336). Male.—Length of body 8-9 mm., of fore wing 9-10 mm. Thorax dark brown, ab- domen yellow-brown, peppered with minute, black dots. Head yellow-brown, with gray streaks on frons around ocelli and on frontal carina; antennae yellow-brown. Pleura and venter of thorax sprinkled with minute, black dots; wings hyaline, often faintly stained with brown at bases; veins brown; legs yellow- brown, partly or completely covered by a sprinkling of black dots. Both dorsum and venter of abdomen sprinkled with black dots; genitalia, fig. 139, yellow-brown, penis lobes with lateral margins straight and inner peri- treme angles blunt; second forceps segment slightly bowed toward apex ; caudal filaments light yellow-brown near bases, becoming white at apexes, articulations dark brown. Female.—Length of body and of fore wing same as in male ; thorax and abdomen lighter colored than in male, causing sprin- kling of black dots to show more clearly; brown on wing veins lighter than in male. N'YMPii.—Length of body 9-12 mm., of caudal filaments 6-8 mm. Uniformly dark yellow-brown, sometimes with small, vague, brown markings on dorsum of thorax; caudal filaments usually uniformly tan, sometimes with faint, brown crossbands. Occipital tubercles of female minute, those of male obsolete, as in figs. 151, 152; max- illary palps completely absent, as in fig. 169; each tarsal claw with 8 to 10 denticles. Posterolateral angles of abdominal segments 2-9 produced as slender spines, those on segment 2 minute, those on segments 3-8 long and slightly curved inw-ard at apexes; tergites 1-7 each with a pair of long, sub- median tubercles, fig. 158, these forming two rows diverging posteriorly; platelike gill of segment 4 operculate, almost or quite covering three posterior pairs of gills; caudal filaments with dense, long setae near apexes. Known from Illinois, Indiana, Maine, Massachusetts, New Brunswick, New York, North Carolina, Ontario, Quebec, Tennes- see, and Wisconsin. Develops in relatively small, shallow lakes. Illinois Records. — Antioch, Channel Lake: Mav 16, 1936, Ross & Mohr, 1 N; May 27, 1936, H. H. Ross, U ; May 16, 1938, B. D. Burks, 1 9 , 1 N. 24. Ephemerella temporalis McDunnough Ephemerella temporalis McDunnough (1924f:74; 1931^:35). Male.—Length of body 7-8 mm., of fore wing 8-10 mm. Thorax bright yellow- brown; abdominal dorsum mostly dark brown; sternum light yellow or tan. Head yellowish tan, eyes light reddish yellow ; each antennal scape and pedicel yellowish tan, flagelluni gray-brown. Wings hyaline, veins in costal region faintly stained with tan; legs bright yellow, apex of each fore femur and fore tibia shaded with tan. Abdominal tergites 2-7 dark brown, often with a vague, transverse, black mark at posterior margin of each, tergites 8-10 yel- I May, 1953 Burks: The Mayflies of Illinois 73 low- or red-brown; sternites light yellow or tan, each sternite usually with an arcuate, transverse row of four black dots. Geni- talia, fig. 143, bright yellow, penis lobes vase shaped, greatly enlarged at bases, second forceps segment slightly enlarged at apex ; caudal filaments yellow to almost white, articulations light reddish brown. Nymph.—Length of body 8-10 mm., of caudal filaments 5-7 mm. Body dark brown, flecked with tan dots; abdomen often with a longitudinal, dorsal tan stripe; caudal fila- ments usually with alternating, broad cross- bands of brown and tan. Head with well-developed occipital tu- bercles, fig. 153; maxillary palps wanting. Thorax lacking dorsal tubercles; each tarsal claw bearing 9 to 12 denticles. Postero- lateral angles of abdominal segments 2-9 produced, spinelike, those borne by segments 2 and 3 minute, fig. 164; abdominal tergites 1-4 each with a pair of finger-like, sub- median tubercles, tergites 5-7 each with a pair of narrow, acute, submedian spines, and segments 8 and 9 each with a pair of rudi- mentary spines, these spines and tubercles forming two parallel rows; platelike gills borne by abdominal segment 4 not entirely covering more posterior gills; caudal fila- ments bearing long, dense setae in apical areas. Known from Georgia, Illinois, Michigan, New Brunswick, New York, North Caro- lina, Ontario, Quebec, and Wisconsin. De- velops in rather small, shallow lakes. Illinois Records.—Freeport: at light, June 11, 1948, Burks, Stannard, Smith, 3$. Grayslake: May 26, 1936, H. H. Ross, 1 N. Havana, Illinois River: May 21, 1895, C. A. Hart, 1 N; shore of Cook's Island, May 17, 1894, C. A. Hart, 1 N; Quiver Lake, June 1-2, 1894, Smith, 1 N; outlet Quiver Lake, June 1, 1895, C. A. Hart, 1 N. Lake County: Cedar Lake, June 19, 1892, Hart & Shiga, 8 N; Fourth Lake, June 16-20, 1892, Hart & Shiga, 14 N; Sand Lake, June 15, 1892, Hart k Shiga, 2 N. Wichert: June 9, 1948, Burks, Stan- nard, k Smith, 1 $ . 25. Ephemerella coxalis McDunnough Ephemerella coxalis McDunnough (1926:186; 1931a:37). Male.—Length of body and of fore wing 7-8 mm. Thorax and abdomen brown, with large, yellow markings; venter light yellow; wings and wing veins hyaline. Genitalia, fig. 144, quite similar to those of lutiilenta, with minor differences in details of structure of peritreme opening. Nymph.—Head with small occipital tu- bercles. Thorax without dorsal tubercles; each tarsal claw with six to nine denticles. Abdominal tergites 1-7 bearing two rows of relatively large, submedian tubercles, fig. 159, these two rows diverging posteriorly, caudal filaments with long setae in apical regions. Known from Georgia, Indiana, North Carolina, Ontario, and Quebec. 26. Ephemerella simplex McDunnough f Ephemerella unicornis Needham (1905:45). Epiiemerella simplex McDunnough (1925c:41; 193l£/:208). Male.—Length of body and of fore wing 6-7 mm. Head dark brown to black, base of each antennal scape surrounded by a yellowish ring; antennae dark brown; eyes deep red-brown. Thoracic dorsum dark brown to black, with minute, light red-brown markings at sutures; thoracic venter vaguely marked with light brown; fore leg black, fading to gray-yellow toward apex of tarsus; middle and hind legs yellow, coxae brown, apexes of tibiae and tarsal segments shaded with faint brown; all wings hyaline, veins stained with brown, those near costal margin of fore wing darker. Abdominal tergites very dark brown, apical tergites vaguely marked with yellow-brown spots; sternum chiefly dark yellow-brown, slightly lighter on sternites 7 and 8; sternite 9 dark brown to black; genitalia, fig. 146, dark smoky brown; caudal filaments uniformly gray- tan, articulations not darker. Female.—Length of body 5-7 mm., of fore wing 7-8 mm. In general, same color as male, but with vertex of head and areas of thoracic pleura at wing bases stained with deep yellow or red and thoracic venter with large, dark yellow areas; all legs dusky yellow, with coxae mostly dark brown; wings hyaline, veins near costal margin of each fore wing stained faintly yellow, other veins hyaline; caudal filaments very light yellow, with basal articulations red-brown. Nymph.—Length of body 6-8 mm., of caudal filaments 4—6 mm. Body and appen- dages extremely broad, flat, and hairy. 74 Ii.i.iNois Natural History Survby Bui.i.etin Vol. 26, Art. 1 General color tan to brown, often with vague, dark brown marks on abdominal dorsum. Caudal filaments with two or three narrow, brown crossbands near base. Head, thorax, and abdomen without dorsal tubercles or spines; maxillary palps well developed; tarsal claws withcuit den- ticles; posterolateral angles of abdominal segments 4-9 produced, spinelike, fig. 162; platelike gills borne by abdominal segment 4 only partly covering more caudal pairs of gills; caudal filaments bearing short, sparse setae throughout. Known from Illinois, New Brunswick. New York, North Carolina. Ontario, Que- bec, and Tennessee. Develops in fairly rapid, moderate-sized rivers. Illinois Record. — Rockton : Rock River, June 25, 1947. B. I). Burks, 5^, 7$. 27. Ephemerella lita Burks Hp/irmn-flla lita Burks (1949:235). Adult unknown. Ny.mph.—Length of body 8 mm., of cau- dal filaments 5.5 mm. General color light tan, with a few small, brown markings; caudal filaments each with a single, narrow, brown crossband near base. Head and body flat, conspicuously hairy, without dorsal spines or tubercles; head semiquadrate, with clypeo-genal margin be- neath each antennal base slightly incised ; maxillary palps well developed; tarsal claws without denticles; posterolateral angles of abdominal segments 2-9 produced, spine- like; platelike gills of abdominal segment 4 semioperculate, only partly covering more caudal pairs of gills, fig. 163; caudal fila- ments bearing relatively few short setae at each articulation, these setae slightly longer in apical area than in basal area of filaments. Known from Illinois. Taken in small or moderate-sized, fairly rapid rivers. Illinois Records. — Dixon: Rock River, May 21-22, 1925, D. H. Thompson, 5 N. Oakwood: Salt Fork River, May 22, 1928, T. H. Frison, 1 N. Rockford: Rock River, June 2, 1927, D. H. Thompson, 1 N. 28. Ephemerella bicolor Clemens Ephemerella bicolor Clemens (1913:336). Male.—Length of body and of fore wing 5-6 mm. Thorax red-brown, abdominal tergites a lighter red-brown, and venter yellow; wings and veins hyaline. Genitalia, fig. 142, with penis lobes enlarged near apexes. Nv.MPH.—Head in male lacking occipital tubercles, fig. 151, but in female having very small ones, fig. 152. Each tarsal claw with 8 to 12 denticles. Abdomen with two rows of dorsal, submedian tubercles diverging to- ward rear, with pair on tergite 5 conspicu- ously more widely spaced than on anterior tergites; caudal filaments each with long setae in apical area. Known from Indiana, New Brunswick, New York, Nova Scotia, Ontario, and Quebec. 29. Ephemerella verisimilis McDunnough Ephemerella virisimilis McDunnough (1930:57; 1931a:65). Male.—Length of body and of fore wing 7-8 mm. Thorax and abdominal tergum dark brown; abdominal venter dark yellow- brown. Wings and veins hyaline. Genitalia, fig. 147, with penis lobes slightly enlarged near apexes. Nymph.—Head with well-developed oc- cipital tubercles. Tarsal claws each bearing 9 to 12 denticles. Abdomen with two rows of dorsal, submedian tubercles which di- verge gradually toward rear; caudal fila- ments with long, dense setae in apical areas. Known from Maine, New Brunswick, Ontario, and Quebec. 30. Ephemerella mhihnella McDunnough Ephemerella minimrlla McDunnough (1931a:63). Male.—Length of body and of fore wing 6 mm. Thorax and basal abdominal tergites mostly very dark brown, with apical two abdominal tergites lighter brown; sternum tan, gradually fading to white on apical two abdominal sternites. Genitalia, fig. 150: penis lobes with a rounded, preapical en- largement on either side, inner peritreme angles acute, and second forceps segment relatively straight. Nymph.—Occipital tubercles wanting in male and vestigial in female; dorsal, sub- median abdominal spines forming two rows evenly diverging posteriorly; caudal fila- ments each with long setae in apical region. Known from Quebec. IV lav, 1953 Burks: The Mayflies of Illinois 75 31. Ephemerella funeralis McDunnoupih Epiicmerella funeralis McDunnough (1925a:210; 1931a:39). Male.—Length of body and of fore wing 6-8 mm. Thorax and abdominal tergites generally red-brown, with sternites lighter red-brown. Wings hyaline, with all veins faintly yellow, and those veins near costal margin of deeper hue. Genitalia, fig. 148: lateral margins of penis lobes nearly straight and parallel near tips, inner peritreme angles acute ; second forceps segment almost straight. Nymph.—Small occipital tubercles pres- ent. Each tarsal claw with 7 to 10 denticles. Abdomen with two rows of dorsal, sub- median tubercles diverging posteriorly; cau- dal filaments with long, dense setae in apical areas. Known from Georgia, Indiana, New York, Ohio, Ontario, Quebec, South Caro- lina, Virginia, and West Virginia. 32. Ephemerella aestiva McDunnough Ephemerella aestiva McDunnough (1931fl:64). Male.—Length of body and of fore wing 6-7 mm. Thorax and abdominal tergites generally very dark brown; basal and apical abdominal sternites shaded with light brown, with median ones white. Genitalia, fig. 149: penis lobes each with lateral margin near apex nearly straight and parallel, inner peri- treme angle blunt; second forceps segment relatively straight. Nymph.—Head with occipital tubercles. Abdomen with two almost parallel rows of dorsal, submedian spines; caudal filaments bearing long setae in apical regions. Known from Quebec. 33. Ephemerella attenuata McDunnough Ephemerella attenuata McDunnough (192Sf:42; 1931(/:209). Male.—Length of body and of fore wing 6 mm. Thorax and basal abdominal tergites very dark brown, apical tergites lighter brown; basal sternites light brown, apical three sternites almost white; wings and veins hyaline. Genitalia, fig. 125, distinct from those of all other North American species: penis lobes fused almost to tips and with a subapical, angulate projection on either side; second forceps segment slightly bowed, and third six times as long as broad. Nymph.—Occipital, thoracic, and dorsal abdominal tubercles present; each tarsal claw with 8 to 10 denticles; first pair of platelike gills semioperculate, as in fig. 162; caudal filaments bearing long setae in apical regions. Known from Maryland, Ontario, and Quebec. BAETISGIDAE This family includes only the genus Baetisca, which was placed in the subfamily Baetiscinae of the family Baetidae by Traver (1935a: 555) and in the family Baetiscidae of the superfamily Heptagenioidea by Ulmer (1933:209). Whereas I agree with Ulmer that Baetisca represents a group sufficiently distinct to be properly considered a family rather than a subfamily, I do not agree that it has heptageniid affinities. The wing vena- tion and the number of clearly differentiated segments in the hind tarsus in the adults plainly show that this group has no near affinities with the heptageniid type. It is one of the mayflies, such as Prosopistoma, which has no known, closely related forms in the Recent fauna. 14. BAETISCA Walsh Baetisca Walsh (1862:378). The compound eyes in the adult males of Baetisca are large, almost contiguous on the meson. The eyes project posteriorly so as almost completely to cover the pronotum. Each of these eyes is composed of a ventral portion m.ade up of small facets and a much larger dorsal portion of large facets. The division between these two portions is not clearly marked, although in life the lower portion is slightly darker than the upper. The compound eyes in the females are widely separated, and each eye, in life, has a verti- cal, anterior, colored stripe near the mesal margin. In the males, the fore leg is about as long as the body; the five-segmented fore tarsus is more than twice as long as the fore tibia, and the fore tibia and fore femur are nearly equal in length. In adults of both sexes, a pair of slender and acutely pointed prosternal projections arise between the fore coxae. Each of the middle and hind tarsi in the males and each tarsus in the females has four clearly differentiated seg- ments. The thorax is quite thickset. 76 Ii.i.iNois Natural History Survey Bulletin \'<)1. 26, Art. 1 The winns of some adults arc washed with red or oranjje, but those of most are hyaline. In the fore win}:, there are quite numerous, weak crossveins, fijz. .^0, numer- ous, short marginal intercalaries, and the outer winn margin is always slightly scal- loped. The median intercalary vein and Mo extend almost to the wing base. There are no cubital intercalaries. Vein lA extends to the outer wing margin, and a series of irregular, weak intercalary veins extends from lA to the anal wing margin. The hind wing is almost circular in outline, fig. 176, has a broad costal projection near the wing base, and numerous weak crossveins and numerous marginal intercalaries; vein M is forked near the center of the wing. The abdomen is stocky in the basal half, but the segments are markedly more slender and elongate from the sixth segment pos- teriorly. The male genitalia, fig. 174, very similar throughout the genus, are composed of a pair of three-segmented forceps and a pair of subcortical penis lobes which are fused on the median line almost to the tips. The apical margin of the terminal abdominal segment in the females has a pair of sub- median, triangular projections with a V- shaped notch on the meson between them. The median caudal filament is vestigial in both the male and female adults. In the subimagoes, the wings are heavily shaded with dark brown or black; white spots surround the crossveins and often two vague, white bands extend obliquely across each wing. The nymphs, the first one of which was described by Walsh (1864), are among the most unique and distinct of all mayfly naiads, fig. 181. In these nymphs, the integument is more heavily armored than in any other Nearctic species. The head is small and hypognathous; a pair of small frontal horns is usually present between the bases of the antennae; and the genae are produced above the bases of the mandibles as a pair of spines or small, flat ledges. These projec- tions of the head vary in size and shape among the different species. The distal margins of the labium and lahrum meet to close completely the mouth opening ante- riorly; the buccal cavity is closed laterally by the mandibles. The labial and maxillary palps each have three segments; the second segment of the labial palp has an apicolateral projection which forms, with the third seg- 179 Fig. 174. — Baetisca ohesa, male genitalia. Fig. 175/1. — Baetisca hajko-vi, gill of first ahclotninal segment. Fig. 175B.—Baetisca hajkovi, gill of fourth abdominal segment. Fig. 175C — Baetisca bajkovi, gill of sixth abdominal segment. Fig. 176. — Baetisca ohesa, hind wing. Fig. 177. — Baetisca laciistris, head of mature nymph, dorsal aspect. Fig. 178. — Baetisca hajko'vi, head of mature nymph, dorsal aspect. Fig. 179. — Baetisca laurentina, head of ma- ture nymph, dorsal aspect. Fig. 180. — Baetisca ohesa, head of mature nymph, dorsal aspect. I May, 1953 Burks: The Mayflies of Ilfjnois 77 ment, a forceps. Each mandible bears, at the apex, two long incisors, a large, tufted lacinia, and a broad, molar surface provided with numerous, lamellate teeth. The hypo- pharynx is large—about one-half as wide as the labrum—and has a pair of broad, thin parapsides. The entire thoracic notum is fused and modified to form a carapace, which covers the thorax and the first five abdominal ter- gites, as well as the anterior part of the sixth abdominal tergite. The legs are rela- tively short and stout, with long, slender, edentate claws which are almost as long as the tibiae. Each of the abdominal segments 1-6 bears a pair of platelike, fissured gills, fig. 175. These gills normally are completely concealed by the thoracic carapace. Ab- dominal tergite 6 has a median, truncated, pyramidal lamina against which the apex of the carapace fits. Each of abdominal segments 6-9 has a pair of blunt, postero- lateral projections. Tergite 9 has also a median dorsal spine on the posterior margin. Tergite 10 has a median notch on the pos- terior margin; this tergite is completely surrounded posteriorly and laterally by the incised ninth tergite. Sternite 9 is produced posteriorly and has a median notch on the posterior margin in both males and females. There are three relatively short caudal fila- ments, each of which bears a dense fringe of setae on both the inner and outer margins. Baetisca was revised by Traver (1931c: 45), and the nymphs were keyed out by McDunnough (1932^:213). Both nymphs and adults were again treated by Traver (1935a: 558), and, since the appearance of Traver's and McDunnough's comprehensive papers, three additional Nearctic species have been described, viz., bajkovi Neave, rogersi Berner, and tho?nsenae Traver. Specific characters for the females of this genus have not yet been found. KEY TO SPECIES Adult Males 1. Wings partly or almost entirely washed with pink 1. rubescens Wings hyaline 2 2. All longitudinal veins of fore wing brown; caudal filaments white, with articula- tions brown 2. laurentina Longitudinal veins of fore wing posterior to Ri hyaline; veins C, So, and Ri lightly shaded with yellow, and bases stained with brown; caudal filaments usually entirely white, basal articula- tions sometimes brown 3 3. Abdominal venter almost completely shaded with brown 3. obesa Abdominal venter white or very pale yellow 4 4. Middle abdominal tergites light brown; fore tibia white, shaded brown at apex; fore wing 10 mm. long 4. bajkovi Middle abdominal tergites dark red- brown; entire fore tibia tan; fore wing 8 mm. long 5. lacustris NVMPHS 1. Mesonotum with both lateral and dorsal spines 2 Mesonotum with lateral spines only, as in fig. 181 3 2. Frontal tubercles of head reduced, virtual- ly wanting, fig. 179. . . .2. laurentina Frontal tubercles of head relatively well developed, fig. 180 3. obesa 3. Frontal projections of head reduced; genal shelf small, fig. 177 5. lacustris Frontal projections of head relatively well developed; genal shelf well developed, fig. 178 4. bajkovi 1. Baetisca rubescens (Provancher) Cloe unicolor Provancher (1876:267), not Hagen. Misidentification. Clof rubescens Provancher (1878:127, 144). New name. Male.—Length of fore wing 8-9 mm. Base and costal area of fore wing and most of hind wing flushed with a pink stain; thoracic notum dark red-brown, abdominal tergites red-brown, and abdominal sternites lighter reddish or yellowish brown; genital forceps and caudal filaments white or pale yellow. The nymph is unknown. The species is known from Quebec. 2. Baetisca laurentina McDunnough Baetisca laurentina McDunnough (1932*: 214). Male.—Length of fore wing 9-10 mm. Compound eyes in life yellow in upper portion, darker yellow, with brown flecks, in lower portion ; head and antennae yellow- brown. Mesonotum dark chestnut brown, darker brown at apex of scutellum ; meso- pleura light brown, sternum dark brown. All legs yellow-brown, with each fore leg slightly darker than others; wings hyaline, with all longitudinal veins of fore wing light brown and crossveins hyaline. Abdominal tergites dark brown; sternites light brown 78 Illinois Natural History Survey Bulletin Vol. 26, Art. 1 to almost white; j;enital forceps tan or reil- brovvn; caudal filaments lijrht yellow or tan, articulations dark brown. Nymi'H.—Length of body 8-10 mm. Frontal tubercles of bead virtually wantinti, only faintly indicated ; each ^ena slightly pro- duced above base of mandible as a small, subtriangular shelf, fiji. 179; dorsal and lateral spines of mesonotal shield long and relatively slender; mesonotal shield relatively long anil slender, with a maximum width, not including lateral spines, two-thirds as great as maximum length. Known from Illinois, Michigan, New Brunswick, Ontario, and Quebec. Develops in cool, fairly rapid streams. Illinois Record. — Aroma Park: Kanka- kee River, June 4, 1947. H. D. Burks, 1 S . 3. liaetisca ohesa (Say) Baftis ohesa Say (1839:43). Male.—Length of fore wing 9-11 mm. Compound eyes tan, lower portion slightly darker; head and antennae yellow-brown. Mesonotum red-brown, darker at apex of scutellum ; thoracic pleura yellow-brown; sternum yellow-brown, becoming lighter to- ward posterior margin. Each fore leg light yellow, apex of femur, of tibia, and of each tarsal segment darkened with yellow-brown; middle and hind legs almost white, brown shading at apex of each tarsal segment; wings hyaline, veins C, Sc, and R, of fore wing brown-shaded at bases, light yellow distad. Abdominal tergites dark brown, be- coming chestnut brown on posterior tergites; sternum light brown, slightly darker on apical three sternites; genital forceps, fig. 174, and caudal filaments usually white or very faintly stained with tan ; basal articu- lations of caudal filaments sometimes brown. Nymph.—Length of body 8-10 mm. Frontal tubercles of head well developed, projecting as a pair of rounded protuber- ances; each gena produced above base of mandible as a triangular ledge, fig. 180; dorsal and lateral spines on mesonotal shield relatively short and stout; mesonotal shield relatively long and slender, with a maximum width, not including lateral spines, two- thirds as great as maximum length. Known from Illinois, Indiana, Manitoba, Michigan. New Hampshire, New York, and Wisconsin. Develops in cool, fairly rapid streams. Illinois Records. — Havana: Illinois River, April 18. 1894, C. A. Hart, I N. .Momence: Kankakee River, June 1, 1937, B. D. Burks, 1 i . Richmond: at light, June 4, 19.^8, Ross & Burks, \$. Rock Island: 20lc', tiys. 18'>- 192 4 4. Vein Sc of hind winij extending nearly or quite to apex of wing, fig. 189 20. Ilabrophlebia Vein Sc of hind winy ending near costal angulation, figs. 190-192 . . 5 5. Costal angulation of hind wing small, rounded at apex, fig. 190; penis lobes simple, without appendages, fig. 214 . 21. Choroterpes Costal angulation of hind wing prominent, almost or quite acute at apex, figs. 191, 192; penis lobes bearing decurrent ap- pendages, figs. 215, 2U> . 6 6. Male forceps base divided into two tri- angular lobes; decurrent appendages of penis lobes projecting anterolateraily, fig. 215; costal projection of hind wing finger-like, stubby at apex, fig. 191 .. . 22. Ilabrophlebiodes Male forceps base entire, not divided into triangular lobes; decurrent appendages of penis lobes projecting toward meson, and a pair of slender appendages aris- ing from forceps base, fig. 216; costal angulation of hind winy acutely pointed at apex, fig. 192 T 23. Traverella Mature Nvmi'hs 1. Gills of first abdominal segment similar in type to gills borne by more posterior segments, as in figs. 194, 196 2 Gills of first abdominal segment of a differ- ent type from gills borne by more posterior segments, as in figs. 193, 195; each gill of first pair filamentous, each gill of following pairs double and lamel- late 6 2. .Abdominal segments 2-9 with postero- lateral spines 19. Thraulodes .Abdominal segments 8 and 9 only bearing posterolateral spines 3 3. Each abdominal gill lamelliform, the margins of each finely dissected to form numerous, long filaments; gills on segments 1-5 bilamellate; gills becom- ing progressively smaller from anterior to posterior abdominal segments 23. Traverella Each abdominal gill not lamelliform, the margins not finely dissected 4 4. Gills on abdominal segments 2-7 each consisting of two clusters of slender filaments borne on a single, narrow stalk, fig. 196 20. Habrophlebia Gills on abdominal .segments 2-7 bifid to bases, each part a very slender la- mella, fig. 194 5 5. Apical margin of labrum only slightly in- dented on meson, fig. 197 18. Paraleptophlebia Apical margin of labrum deeply indented on meson, fig. 198 22. Habrophlebiodes 6. Each gill of pair borne by first abdominal segment a single filament; apical ex- tensions of gills on segments 2-7 some- what spatulate at apexes, fig. 195. . . . 21. Choroterpes Each gill of pair borne by first abdominal segment bifid at apex; apical extensions of gills on segments 2-7 slender, acute at apexes, fig. 193 12, Leptophlebia 17. LEPrOPHLEIilA Westwood Leptophlebia Westwood (1840:31). Blasturus Eaton (1881:193). Eupliyurus Bengtsson (1917:177). In accordance with the researches of Ide (19.?5a: 12,?), the American species formerly placed in Blasturus are now placed in Lepto- phlebia. It may he noted that Banks (1900: 245) published this synonymy much earlier. The members of this genus are medium to large mayflies with predominantly dark yellow-brown bodies. The fore tarsus in the males varies from one to one and two-thirds times as long as the fore tibia. The wings, figs. 185, 196, are clear or partly stained with brown, and all veins and most cross- veins are brown. In the fore wing, the posterior branch of the outer fork (vein R,,) is sharply bent posteriorly near the base, vein M., diverges from Mj in the subbasal region, the basal costal crossveins are weak or wanting, and there are two long, cubital intercalary veins. The hind wing has no costal angulation, and vein M is forked near the base of the wing. The male genitalia, fig. 200, are quite uniform in structure throughout the genus. The genital forceps arise from a medianly fissured base and have four or five segments, of which the apical two are minute. The penis lobes are fused on the meson at the bases only; each penis lobe bears a stout, mesal, decurrent appendage. The position of the apexes of these appendages determines whether they look like a "scarf" or a "hood"; actually the structure of these ap- pendages is very similar throughout the genus. The terminal abdominal sternite in the females has a triangular, median notch on the posterior margin. The three caudal filaments may be equal in length and thick- ness or the median filament may be slightly shorter and weaker than the cerci. The stout-bodied nymphs, fig. 199, are vigorous swimmers. The thorax and ab- domen are slightly flattened on the dorsum, but the head is held almost in a hypognathous position. Each of the maxillary and labial May, 1953 Burks: The Mayflies of Illinc 85 Fig. 199.—Leptophlebia sp., mature nymph, dorsal aspect. palps has three segments. Each antenna is longer than the head and thorax combined. Each tarsal claw has two rows of ventral denticles, a long row from base to near the tip on the outer side, and another, shorter row near the tip on the inner side. Gills of the first abdominal segment are bifid and filamentous, fig. 1935; the gills on segments 2-7 are double and lamelliform, figs. 193^^ and C, each lamella having a terminal, fila- mentous extension. Each of the three caudal filaments is slightly longer than the head and body combined. In this genus, specific characters for the females and nymphs have not yet been found. KEY TO SPECIES Adult Males 1. Abdominal tergites 2-7 white, with dark spiracular dots 1. johnsoni Abdominal tergites 2-7 partly or almost completely covered by dark brown shading on a tan background 2 2. Fore wing with apical one-fourth to two- fifths shaded with brown, fig. 185; oc- casionally a spot at outer apical angle of wing hyaline 2. nebulosa Fore wing completely hyaline except for faint, brown shading in stigmatic area, fig- 186 3. cupida 1. Leptophlebia johnsoni McDunnough Lcptuplilehia jo/insoni McDunnough (1924c-: 73). Blasturus gracilis Traver ( I932rt: 133). M.ALE.—Length of body and of fore wing 8-9 mm. Head very dark, glossy brown, with eyes slightly lighter brown. Thorax dark brown to black on dorsum and light brown to tan on pleura and sternum; wings hyaline, with veins and most crossveins dark brown, and each fore wing with a light brown cloud covering stigmatic and outer apical areas. Abdominal segments 2-7 white, with dark brown, or black, spiracular dots and tan ganglionic marks; segments 8-10 dark brown; genital forceps white, penis lobes yellow; caudal filaments tan, with articulations dark brown. Known from Connecticut, Massachusetts, New Hampshire, New York, North Caro- lina, Ontario, and Quebec. 2. Leptophlebia nebulosa (Walker) Palingenia nebulosa Walker (1853:554). Poiamantlnis odonatus Walsh (1862:372). No authentic Walsh material of odonatus is known to be in existence, but the charac- ters given in Walsh's original description of the species certainly indicate that odonatus is a synonym of nebulosa. When Spieth (1940:327) examined the type of nebulosa in the British Museum, he found no reason to alter the concept of the species as currently identified. Male.—Length of body and of fore wing 10-12 mm. Head dark brown, eyes slightly 86 Ii.i.iNois Natural History Survey Bulletin Vol. 26, Art. 1 lighter brown. Kntire thorax very dark brown, almost black, each fore leg brown, middle and hind coxae brown, rest of middle and hind legs tan; wings hyaline, veins and most crossveins tan or brown, crossveins toward posterior margin in either wing often hyaline, stigmatic crossveins of each fore wing extremely numerous, anastomosed, a brown cloud covering outer, apical one- fourth to two-fifths of fore wing, fig. 185, but sometimes with extreme outer, apical angle hyaline, making wing appear to have a broad subapical, brown crossband. Dorsum of abdomen almost or entirely dark brown, sometimes becoming tan along lateral mar- gins of tergites, and often with a pair of submesal, short, lunate, tan marks present at anterior margin of each tcrgite; sternites 1 and 2 light brown, sternites 3-8 tan or yellow with, sometimes, vague brown shad- ing, sternites 8 and 9 brown; genitalia, fig. 200, with forceps tan and penes brown ; caudal filaments brown, articulations darker brown. Female.—Length of body 10-12 mm., of fore wing 12-14 mm. Color much as in male, but somewhat lighter. Head with yel- low shading on each side, near eyes. Thorax with yellow areas on pleura, with sternum mostly yellow-brown; wings without brown shading. Dorsum of abdomen as in male, sternum entirely tan or yellow-brown, apical two sternites always a little lighter than others; caudal filaments tan or light brown, articulations darker brown. Known from northeastern and midwestern states and southeastern Canada. Develops in ponds or in the still eddies along the banks of streams. Illinois Records. — Chesterville: April 15-May 1, 1936, Ross & Mohr, 9$. Dan- ville: May 9, 1926, T. H. Krison, U. Georgetown : April 14, 1930, Frison & Ross, 4i, 29. Havana: April 15, 1898, Hart, \6 : April 18, 1894, Hart, \6 ; April 21, 1898, Hart, 1 6 ; April 22, 1898, Hart, 116, 7 9 ; April 24 & 25, 1898, Hart, 16 6 , 10 9 ; April 28 & 29, 1898, Hart, 1 '"^''P'"Plilfl>iia 'Volilans, male genitalia. Fig. 210.—Paraleptophlehia guttata, male genitalia. Fig. 211.—Paraleptophlehia stric/ula, male genitalia. 90 Illinois Natural History Survey Bulletin Vol. 26, Art. 1 Penis lobes each with a large, decurrcnt appendage, fig. 207 6. Ontario 7. Penis lobes without decurrcnt appendages, fig. 2(»8 7. mollis Penis lobes with decurrcnt appendages, figs. 209-211 .8 8. Penis lobes without apicolatcral projec- tions; decurrcnt appendages slender, bifid at apexes, fig. 209 8. volitans Penis lobes with apicolateral projections; decurrcnt appendages not bifid at apexes -9 9. .Abdominal tergites 2-7 white, with spiracular dots; mesal apical angles of penis lobes divergent, fig. 210 9. guttata Abdominal tergites 2-7 white, with spiracular dots and a large, brown spot near each posterolateral angle; mesal apical angles of penis lobes converucnt, fig. 211 10. strigula Matire Nvmphs 1. Gills borne by abdominal segments 3-5 dividing into two branches at a point at least one-third the distance from base to apex of gill; tracheae of these gills with numerous, prominent, lateral branches 2 Gills borne by abdominal segments 3-5 divided into two branches at a point not more than one-sixth the distance from base to apex of gill; tracheae of these gills with only a few, minute, lateral branches 3 2. .Anterior margin of labrum slightly in- dented on meson; each gill of abdominal segments 3-5 divided at a point about one-third distance from base to apex of gill 7. mollis .Anterior margin of labrum not indented on meson; each gill of abdominal seg- ments 3-5 divided at a point about one- half distance from base to apex of gill 5. adoptiva 3. Abdominal venter with a pair of longi- tudinal, sublateral brown bands 3. praepedita Abdominal venter without sublateral bands 4 4. Only abdominal .segment 9 with postero- lateral angles produced as spines. . . .5 Both abdominal segments 8 and 9 with posterolateral angles produced as spines _ .6 5. .Abdominal segments 2-6 each with a black streak along either lateral margin 10. strigula Abdominal segments 2-6 with only a small, black spot near base of each gill 9. guttata 6. Gills borne by abdominal segments 3-5 with long, sparse, marginal hair 8. volitans Gills without marginal hair 7 7. Tibiae light yellow, with brown band in middle and at base of each 1. debilis Tibiae light yellow or tan, with brown shading at bases only 8 8. Combined length of second and third seg- ments of maxillary palp one and one- half times as great as length of first segment 6. Ontario Combined length of second and third segments of maxillary palp equal to length of first segment . . .2. moerens 1. Paraleptophlehia dehilis (Walker) liaetis dehilis Walker (1853:569). I.eptophlrhia mollis .Needham (1908:189), not Katon. Misidentification. I.iptnplilrliia separata Ulmer (1920tf:27; 1921:255). Male.—Length of body and of fore wing 8-9 mm. Head, thorax, and apex of abdomen dark brown, abdominal segments 2-7 white, with transverse, brown lines at posterior margins of tergites; wings hyaline, with tan longitudinal veins and colorless crossveins; genital forceps, fig. 201, a faint tan, with penis lobes slightly darker; caudal filaments white. Known from the northern states and the southern part of Canada. 2. Paraleptophlehia moerens (McDunnough) Leptophlchia moerens McDunnough (1924/':94). Male.—Length of body and of fore wing 5.5-6.5 mm. Head dark brown, almost black ; eyes in life brown ; antennae dark brown, each becoming hyaline at apex of flagellum. Thorax dark brown; fore leg light brown, with femur and tibia shaded with dark brown; middle and hind legs light brown, with coxae dark brown, femora and tibiae shaded with dark brown, and tarsi white; wings hyaline, with faint brown staining at base of fore wing, veins and cross- veins colorless. First abdominal segment dark brown; second tergite shaded with light brown, with dark brown crossband at pos- terior margin; tergites 3-6 white, with dark brown crossband at posterior margin of each; apical three segments chestnut brown; sternites 2-6 white, with large, median, orange-tan spot on each ; forceps base brown, forceps, fig. 203, tan, penis lobes yellow- brown; caudal filaments white. Female.—Length of body and of fore wing 7 mm. Head and thorax red-brown, lighter than in male; legs light brown, with dark brown shading at base of each tibia ; wings very faintly stained with tan, and M: 195.^ Burks: The AIayflies of Illinois 91 longitudinal veins of fore wing stained a faint yellow-brown. Abdomen uniformly red-brown, each segment with posterior margin slightly darkened; terminal abdom- inal sternite with a relatively shallow, broad, rounded, median excavation on posterior margin ; caudal filaments a faint yellowish tan. Nymph.—Length of body 7-8 mm. Head light yellow-brown, with lateral areas near eyes shaded with red-brown. Thorax light brown, yellowish laterally; legs light yellow- genitalia, figs. 202, 204, light brown; caudal filaments uniformly tan. Female.—Length of body 5-6 mm., of fore wing 5.5-6.5 mm. Coloration similar to that of male, except that red-brown re- places dark brown, and tan replaces light brown; all crossveins of fore wing, except those in anal and cubital areas, tan; cubital and anal crossveins of fore wing, and all crossveins in hind wing, hyaline ; posterior margin of seventh abdominal sternite pro- duced posteriorly to form a long, pointed Fig. 212. — Paraleptophlrhia praepedita, mature nymph, lateral aspect. brown, with brown shading near apexes of femora. Abdomen light brown, each tergite with two pairs of vaguely defined, light yellowish spots ; gills hyaline, tracheae gray, with only a few, minute, lateral branches; posterolateral angles of tergites 8 and 9 produced as spines; caudal filaments light yellow-brown. Known from the northeastern and mid- western states and eastern Canadian prov- inces. Illinois Record. — Herod: Branch Big Grand Pierre Creek, May 2, 1946, Burks & Sanderson, 1 i . 3. Paraleptophlebia praepedita (Eaton) Leptophlehia praepedita Eaton (1884:99). ALale.—Length of body and of fore wing each 4.0-5.5 mm. Head very dark brown, almost black ; eyes in life dark red-brown ; antennae brown, each becoming hyaline at tip of flagellum. Thorax very dark brown, with yellow-brown markings on pleura; legs usually uniformly light brown, femora some- times slightly darkened ; wings hyaline, each fore wing slightly brown-stained at base, longitudinal veins tan, crossveins colorless. Abdomen usually uniformly brown, middle segments sometimes slightly lighter brown on dorsal meson and at anterior margins; ovipositor; posterolateral angles of terminal sternite acuminate, median emargination of posterior margin deep and triangular; caudal filaments tan. Nymph.—Fig. 212. Length of body 5-7 mm. Head and body tan, vaguely marked with light yellow on dorsum of thorax ; legs yellow, shaded with tan near apexes of femora, in middle of tibiae, and near bases of tarsi; abdominal tergum tan, marked with light yellow on meson and near postero- lateral angles of each tergite ; abdominal venter yellow, with longitudinal, tan bar parallel with and near to each lateral margin; gills hyaline, central tracheal stripes purplish gray; posterolateral angles of ab- dominal tergites 8 and 9 produced as spines; caudal filaments uniformly tan. Known from the northeastern and mid- western states and eastern Canada. This is the commonest species of Paraleptophlebia in Illinois. Illinois Records. — Diona: June 7, 1941, Ross &: Mohr, 1 i . Eddyville: Lusk Creek, May 16-17, 1947, B. D. Burks, \$. Fox Ridge State Park: May 13-17, 1938, Ross & Burks, 6 5 , 1 9 , 1 N ; May 25, 1942, Ross & Riegel, U , 2 N. Herod: May 2-9, 1942, Burks & Mohr, A$, 79, 16 N; May 13, 1939, Burks & Riegel, 2$ ; May 27, 1942, B. D. Burks, 71 <5 , 8 9 ; Mav 2, i946, Mohr 92 Illinois Natlral History Survey Bulletin Vol. 26, Art. 1 & Burks, \S. MoNTicELLO: June 6, 1947, Jack Warner. .? S . Muncie: May 24. 1914, U. Oakwood: May 22, 1942, Ross & Burks. b3 : May 28, 1948. Burks & Evers, M: May 29. 1936. Ross & Mohr, 2$. Richmond: June 14. 1938, Mohr & Burks. 1 of fore wing detached at base from 'stem of M, figs. 31, 220-222; hind wing greatly reduced or wanting entirely; hind tarsus with only three clearly defined segments, fig. 15 Baetinae, p. 113 Vein M-. of fore wing not detached at base from 'stem of M, figs. 217-219; hind wing well developed; hind tarsus with four clearly defined segments, figs. 18, 20 2 2. Gill remnants present at base of rudi- mentary maxilla and at base of fore- coxa Isonychiinae, p. 108 Gill remnants absent Siphlonurinae, p. 98 Mature Nymphs 1. Each abdominal gill composed of a plate- like dorsal element and a ventral fibril- lar tuft, fig. 225; fore coxa and maxilla with gill tufts. . .Isonychiinae, p. 108 .AH abdominal gills platelike; gills usually single, but, when double, both elements of each gill platelike, figs. 223, 224, 226-228; fore coxa and maxilla without gills _. 2 2. Posterolateral angles of each apical ab- dominal tergite prolonged as thin, flat spines, figs. 2405, 247, 254; labrum with anterior margin entire or with a broad, median, V-shaped notch, fig. 229 Siphlonurinae, p. 98 Posterolateral angles of apical abdominal tergites not prolonged as spines, figs. 266, 298; labrum with a median, scjuare notch, fig. 231 Baetinae, p. 113 SIPHLONURINAE The subfamily Siphlonurinae, as here de- fined, corresponds very closely to Ulmer's family Siphlonuridae (19.3.3:209). In the Siphlonurinae, each compound eye in the adult males is made up of an upper portion composed of large facets and a lower portion of smaller facets, but the two por- tions of the eye are not distinctly separated, fifl. 241. The fore tarsus in adult males is always much lonjjer than the fore tibia. Gill remnants are wanting on the head and thorax of adults of both sexes. The fore wing in this subfamily is readily dis- tinguished from the fore wing in all other mayflies, in that the cubital intercalary veins form a series of parallel, often sinuate but usually not branched veins extending from vein CU| to the anal margin of the wing, and in that vein Cuj is straight throughout its length, fig. 219. In the hind wing, vein M is either not forked or forked in the basal half of its length. In many species, the wings are wholly or partly shaded with brown, yellow, or tan, with prominently colored veins and crossveins. In the adults, the median caudal filament is always vestigial. The vigorous, fishlike nymphs, figs. 2405, 247, of the members of this subfamily are strong and rapid swimmers, almost always living in rapidly flowing water. The tarsal claws of the nymphs are long and slender, but are always shorter than the tibiae, fig. 26. Gills are borne only by the abdomen, and these gills are platelike and usually single, but when they are double both parts of the individual gill are platelike. There are always three well-developed caudal fila- ments. Each cercus has long setae on the inner side only. The nymphs of Siphlonurits have been shown to be at least in part pre- daceous (Morgan 1913:386). The struc- ture of the mouth-parts of the nymphs of another genus, Parameletus, indicates that it also may be predaceous. KEY TO GENERA Adults 1. Abdominal segments 5-9 with broad, flat, lateral expansions, fig. 233; median ventral spine present on mesosternum and metasternum . . .24. Siphlonisca Abdominal segments without broad, later- al expansions; no median ventral spines present on thorax 2 2. Hind wing with an acute costal angulation, and vein M forked near base, fig. 237. 25. Ameletus Hind wing with a blunt, or with no, costal angulation, and vein M either not forked or forked well distad of the base, figs. 218, 219 3 3. Vein M of hind wing simple, not forked, fig. 218 26. Parameletus Vein M of hind wing forked, fig. 219. ... _ 27. Siphlonurus I May, 195.^ Burks: The Mayflies of Illinois 99 r.. M. ' ' —"—» i_iji_i_j>_>-— u •'"I "2 Cu, M, **' 221 ^^£T^=-^^ 222 Fig. 217.—Isonycliia rufa, wings. Fig. 219.—Siphlonurus rjuebecensis, wings. Fig. 218.—Paramelctiis midas, wings. (After Fig. 220. — Baetis prop'inquiis, wings. Traver.) Fig. 221.- — Calli/>ae(is fluctuans, wings. Fig. 222.—Callibactis ferrugineiis, wings. Mature Nymphs extensions on the margins of abdominal seg- 1. A stout, median, ventral spine on meso- ments 5-9 of the adults, fig. 233, and on all and metasternum, . . . .24. Siphlonisca abdominal segments of the nymphs, fig. 234. IN'o median ventral spmes on thorax. . . 1 . . . ... , 2. A conspicuous, transverse pecten of ^ midventral spme is present on the meso- spines present on margin of each max- sternum and metasternum in both the ilia, fig. lAOA 25. Ameletus nymphs and the adults. The abdominal gills No pecten of spmes present on maxdla. .3 ^^ ^^^ j^^ ^^^ ^j j^ ^^j platelike, with J. Apical segment or labial palp and an .,.,,. , r^. apposed, thumblike projection of penul- the margins slightly irregular. 1 he median timate palp segment forming a forceps, caudal filament is well developed in the fig- 230 26. Parameletus nymphs, but is vestigial in the adults. Labial palp not forceps-hke at ap« .^^^^ Siphlonisca most closely resembles Onisci- 27. Siphlonurus ^^^^^^ McLachlan (1873:108; 1874:139), 24. ^/P//LOA^/^-C^ Needham described from New Zealand. Siphlonisca aerodromia Needham (1909: Siphlonisca Needham (1909:71). 71)^ known from New York, is the only This strikingly distinct genus is at once described species. The male genitalia of this recognizable because of the wide, flat lateral species are shown in fig. 232. 10.) Im.ino:3 Natural History Survey Bulletin Vol. 26, Art. 1 2S. A MELETUS Eaton AmfUlus Katon (1835:210). In the members of this fienus. each com- pound eye. in both the males and females. has a slightly oblique, contrastingly colored band extending across the outer surface, fig. 2.^5. This band is visible only in freshly killed or living specimens, as the color pat- tern of the eyes quickly disappears after 227A 227 B 227 C 228 A 228 B Fig. 222>A.—Siplilonunis marslialli, gill of frst abdominal segment. Fi}«. 22iB.—Siphlonurns mars/ialli, gill of seventh abdominal segment. Fi)i. 223C — Siphlonnrus marslialli, gill of fifth abdominal segment. Fig. 224. — Siphlonnrus alternatus, gill of fiftfi abdominal segment. Fig. 225/1. — Isonychia sp., gill of first abdominal segment. Fig. 22SB.—Ismiychia sp., gill of seventh abdominal segment. Fig. 225C. — Isonyi Ilia sp., gill of fifth abdominal segment. Fig. 2264. — Callihaetis skokianus, gill of first abdominal segment. Fig. 226B.— Callihaetis skokianus, gill of seventh abdominal segm:nt. Fig. 226C.—Callihartis skokianus, gill of fifth abdominal segment. Fig. 227A.—Amrlrtus lir.eatus, gill of first abdominal segment. Fig. 227B.—Ameletus linraius, gill of seventh abdominal segment. Fig. 227C. — Ameletus lineatus, gill of fourth abdominal segment. Fig. 228/1. — Raetis hrunneieolor, gill of first abdominal segment. Fig. 228B. — Baetis hrunneieolor, gill of seventh abdominal segment. Fig. 228C — Baetis hrunneieolor, gill of fourth abdominal segment. 228 C I May, 1953 Burks: The Mayflies of Illinois 101 ,y:<^M'X, 232 Fig. 229. — Sipltlonui us marslialli, labium of mature nymph, dorsal aspect. Fig. 22iO.—P