Bulletin STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE NATURAL HISTORY SURVEY STEPHEN A. FORBES. Chef Vol. XV. BULLETIN Article VL Illinois River Bottom Fauna in 1925 BY ROBERT E. RICHARDSON PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA. ILLINOIS October. 1925 STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION A. M. Sheltox, Director BOARD OP NATURAL RESOURSES AND CONSERVATION A. M. SiiELTON', Chairman William Trelease, Biology John W. Alvord, Engineering John Coulter!, Forestry Kendric C. Babcock, Representing the Edson S. Bastin, Geology President of the University of lUi- William A. Noyes, Chemistry nois THE NATURAL HISTORY SURVEY DIVISION Stephen A. Forbes, Chief ScHNEpp & Barnes, Printers Sprinofikld, Iix. 1925 34185—900 CONTENTS PAGE Introduction ^ 391 Summary 392 Illinois River above Peoria Lake, La Salle—Chillicothe, 44 miles 393 Peoria Lake, Chillicothe—P. P. U. Bridge, 20 miles 394 Illinois River below Peoria, P. P. U. Bridge—Beardstdwn, 71.5 miles 405 The missing small bottom animals of the 1913-1915 species lists, apparently exterminated some time between 1915 and 1920. Head of Peoria Lake to Beardstown 410 Small bottom invertebrates of Illinois River and Peoria Lake, La Salle to Beardstown, 1923 414 Pre-1920 bottom species recently missing from Illinois Rivei" and Peoria Lake dredge hauls 418 Article V'I.—The Illinois Riz'cr Bottom Faiiiia in /p-'j?. Bv Robert E. Richardson. The i)resent paper is based on one hundred and fifty Petersen sampler collections taken in the Illinois River and Peoria Lake between June and September 1923 ; includinj^- •H> taken between La Salle and the head of Peoria Lake; 75 in the lake or its entrance, outlet, or connecting- '"narrows" ; and 40 below the lake and between Peoria and Beardstown. The subdivision of the river and lake into zones follows that in the article on the 1922 bottom fauna as respects Peoria Lake, emphasizing distance from the channel center rather than depth, and recognizing three subdivisions as follows: (1) a central, imaginary, channel zone of about 700 feet average total width; (2) to either side and adjacent to this an intermediate zone extending outwand to the 1500 foot line, on either sitle of the channel center; and outside of this, where the width permits. (:?) an outer zone extending anywhere from somewhat more than 1500 to more than -1800 feet beyond the mid-channel line at recent summer levels with normal rainfall. In the river the so-called intermediate and outer zones corres])ond for the most part, except where the river is very shal- low, to the zones of 4 to 7 and 1 to 3 feet as used in preceding papers, reference being to recent normal summer levels. The subdivision of the species on the basis of degree of tolerance also follows in main features that of the 1923 paper, which recognizes, in general, three greater groups, as follows ; Group I. Pollutional or more or less tolerant species, including all recent tubificid worms, leeches, and midge larvae of Peoria Lake ; and a number of more than ordinarily tolerant snails belonging chiefly to the sphaeriid genera Musculium and Pisidium. The basis of inclusion in this group has been chiefly the fact of survival in Peoria Lake through 1920, a short time before which year a sizable list of the more .sensitive of the members of the old bottom population seem to have been wholly exterminated. P'or the distinction between the words pollutional and tolerant as used above and elsewhere in this ])aper, and the general align- ment of terminoolgy with that of our 191;! paper on the biology of the Upper Illinois*, see the paper on changes in the bottom fauna of Peoria Lake, 1920 to 1922t. Group II. Cleaner preference species, including principally current- loving forms of snails, Bryozoa. insects, and Crustacea, that have per- sisted in Peoria Lake or in the river shortly southward through and. • But. III. state Kab. Nat. Hist.. Vol. IX.Art. 10. .Tune. I91.'!. t Hill III. .'^tale .Vat. Hist. Siirv.. Vol. XV. Art. V. 1!I25. 392 since l'J2(), usually near shore cir in unusually good current, but where all of the species in Group III have disappeared. Group III. Missing members of the old bottom fauna, as of our lists of 1913-1915, including snails of the families Viviparidae and Amni- colidae, chiefly ; insects or insect larvae or nymphs of the orders Ephe- merida, Odonata, Hemiptera, Neuroptera, and Coleoptera ; and various other small bottom animals. The word pollutional as here used corresponds roughly to Kolkwitz's term "mesosaprobic" and to Forbes and Richardson's term "pollutional". as used in the 1913 paper on the Illinois River. Both in its use and in that of the word "tolerant" (rather than "contaminate") it has been my purpose to attain greater flexibility than might be expected with the customary restricted use of these or similar terms ; and by the use of the latter term, more especially, to express better the breadth of range, merg- ing preferences, and adaptability of the not inconsiderable group of species which find their true position, quite unbounded by hard and fast lines, almost anywhere between pollutional and strictly clean-water forms. SUJIM.\UV In the 44 miles of the Illinois River above Peoria Lake examined in the summer of 1923 all of the bottom organisms taken belonged to the more strictly pollutional or unusually tolerant kinds : the most of them being small worms, at least one variety of which has previously both in Illinois and elsewhere been found to be characteristic of septic sludge. In this portion of the river the "sludge worms" were found to be most abundant outside the channel, where there is greatest sedimen- tation after floods. The small bottom animals taken in 11123 in the broadly expanded 20-mile section of river between Chillicothe and the foot of Peoria Lake were with a few exceptions jiollutional or more or less tolerant forms, in variety, abundance, and dispersal, showing no essential change since the summer of 1922. Toward shore on the west or sand blutT side of the first 14 miles of this 20-mile section, and in the faster current of the upper and lower "narrows" or adjacent waters several less tolerant to fairly clean prefer- ence species were taken, as they were also in 1920 and 1922: and these showed some evidence of increase both in variety and numbers within their recent range as thus localized. In about 71.5 miles of river below Peoria studied in 1923 enumera- tions showed a clear though irregular wards of half a dozen varieties of Tubiticidae, small worms some of which are characteristic of .septic sludge; two or three varieties of leeches ; a similar number of kinds of chironomid larvae, of which one, 394 Chirononms dccorus, has a previous definite record of pollutional habit ; and three species of sphaeriid snails, of which one, Musculhim transvcr- siim, has previously been found in company with tubificid worms where their numbers exceeded 40,000 per square yard. Both in the channel and the outer zones of the river between La Salle and Henry, in the first 38.5 miles of the section dredged in 1923, nothing at all but tubificid worms were taken. Miisculium transz'ersum was taken at most stations between the Henry dam and Chillicothe (15.5 miles) ; the few kinds of midge larvae and leeches not until Lacon or below : and the two less tolerant Sphaeriidae only at or within two or three miles of Chillicothe. The bulk of the tubificid worms taken in the more polluted reaches. as in upper Peoria Lake in 19-?2 and 1923, were not identified as Tttbifc.v tubifcx, the common pollutional form recorded in Europe, but as species of the genus Limnodrilus. The largest numbers of all tubificid worms combined, and of Tubifcx tubifcx and the two principal species of Limnodrilus taken singly, per unit of bottom area, did not occur in the river channel, but in the shal- lower water close to or outside the 3-foot line, where conditions favor the greatest sedimentation. Peoria Lake, ChiUicothe—P. P. U. Bridge*, 20 Miles In Peoria Lake in 1923 rather rapid increase is visible in the variety of the small bottom fauna as we proceed southward, as well as increase of the less tolerant forms in identical areas as compared with 1920 and 1922. But it is equally clear that the increases in kinds and in abun- dance of the less tolerant groups are greatest, and that they in fact show a strong tendency to be localized, either (1) quite close to shore; (2) in the faster current of Peoria Narrows or other essentially river situations included in the comparisons; or (3) in the rather limited area represented l)y the southwest third or less of the lower lake that lies between Long Shore Beach and Al Fresco Park. Except at a few stations in swifter current*, also, numbers and bulk of the species with greatest preference for clean bottom are uniformly nuich smaller per unit of bottom area than are the numbers and volume of the tubificid worms and others of the pollutional or more tolerant groups taken alongside of them. * Where bulky growths of sponge or Bryozoa occurred. 395 p. 3 a i 2 > O 3 o a 3 O u o, 3 -f = g 5 o -A CO S I 3 c P. 3 O cs 3 C5 a 3 O b o a 3 o o i; o t>, ~ m S o t. , 3 J3 o a « ac 1- t. 396 o u O i!" m as o 03 ca k4 «; c3 M O m c Id «. w 397 p. 3 O u o =1 Cfl a; •- Si cS O M c 2 ! w Q 3 I ^ UQ — • 398 p. s o s-< O ^ O 3m m OM 03 t- < a o 03 . 399 It is noted both of Tubifcx tubifcx and of the more abundant species of Limnodrihis that, quite contrary to the findings in the river above Chiilicothe in 1923, their numbers in upper and middle Peoria Lake ran about as high if not higher in the cliannel than in either of the outer zones. This is, however, in agreement with such information as we have about velocities, which evidently permit much more sedimentation in the lake channel during flood recessions than can ordinarily take place in average river above the lake. The sludge worms as a whole showed an irregular decline southward of the upper lake in 1923, both in the channel and in the outer zones, with exception of some upturn in the figures at Peoria Narrows and the U. S. Slips, which are unexplained. Unworked out specific dift'erences might be concerned here. It is at least known that not all species of Limnodrilus. or even Tubifex, forthat matter, are equally tolerant of or partial to polluted bottom. Compared with 1922, both the Tubificidae and the very tolerant sphaeriid snail {M. transvcrsmn) showed conspicuous decline in num- bers in the upper lake in 1923 collections. This was true in all zones in the upper lake and should, it would seem, mean improvement. In the middle lake, however, numbers both o.f the worms arid of the snail showed a tendency to equal or even to exceed the numbers per square yard of bottom area found in 1922. Perhaps efl^ects of seining, and of varying amounts of feeding by bottom-ranging fishes might be concerned in these irregularities. If they are, evidence such as we have on the variety of bottom-dwelling forms present, and their preferences, are of more importance in the definition of degrees of pollution than such numbers are likely to be. Peoria Lake, 1923 Compared with 1922. Av. Nos. veb, Sq. Yd. 400 Peoria Lakk. 1923 Comparkd with 1922. Av. Xos. per Sq. Yd. 401 abundant in collections from near the lower end of the middle lake, where snails and some of the other less tolerant groups were taken in variety. Incompleteness of the determinations has also jiroljably included among the Chironomidae, which are in the following tables all listed as at least mildly tolerant, some species which are essentially cleaner water forms. But if that is the case, it does not probably invalidate the comparison of 1953 species lists with those of 1922 for evidence of increase in cleaner-preference species, since most of the 108;5 larvae seem to have counterparts in the 1!)22 (or 1920) collections. Study of the dates of collection of this group in the summer of 1933 shows that from IMossville north decidedly more Chiroiiomidae occurred in July and August than in June collections; while in the lower half of the middle lake the largest ntmibers were recorded in June in one cross-section (opposite Long Shore Beach) and in July or August in two others (opposite Towhead and Al Fresco). Cbironomus pliiiiiosus var., a supposed ])ollutional species, occurred in all three months, and C. dcconis. another with a similar record, occurred both in June and August. On the face of things to be taken as evidence of improvement in the muds since 1922 would seem to be the sizable increases shown in the twelve-month period in all three of the sections of Peoria Lake in both the total numlier of bottom species of all kinds taken and in the number of group 11* kinds (i. "e., current-loving snails, young mussels, other insects than Chironomidae, and miscellaneous associated species such as sponges. P>ryozoans. Planarians, etc.). Combining all collections from all zones, and taking account of these gross figures only, without regard to ])Ossible special or localized conditions at points of e.xact occurrence of grouj) II species, it is found that in the upper lake in 1923 there were 5 group II kinds taken as compared with one in 1922 ; in the middle lake T as compared with none at all ; and in the lower lake, including Peoria Narrows and P. P. U. Bridge in 1922 and those two stations and the McKinley Bridge in 1923, 11 kinds as compared to 7. Corre- spondingly, of the total number of all kinds taken, it is found that it rose in the upper lake from ]S to 24-2.") in the year; in the middle lake from 23 to 29-30; and in the lower lake from 21 to 24. Since the total number of collections in all zones combined was very nearly the same in all three lakes in 1922 and 1923 (U. L. : 1922, 23; 1923, 21; M. L. : 1922. 30; 1923. 30; L. L. : 1922, 18; 1923, 24). at least the changes in the totals would not be expected to have been due to changes in thorough- ness of collecting. Further favoring improvement, particularly in the extra-chaimel zones of the upper and middle lakes, where the greatest increase in group II s])ecies occurred, would appear to be the fact that the increases in the number of species in those areas in both lakes took jilace in the face of decreases in the number of collections between 1922 • In text and t.ibulatlons that foUow. the No. II (troup l.s .set over aealn8t group I. made up of the m<»re or less delinitely poUutfcinal or tolerant groups of tubincid norms, leeches, midge larvae, and .sphaerlld or other snails which have ".mood the racket" in I'eorla Lake in the last few years. 402 and 1923 (U. L. : ex-channel, 1923, 20; 1923. 9; M. L. : ex-channel, 1922, 27; 1923, 20). Points of exception that must be noted are, however, several, as will be seen from what follows : First it is noted that the two species of snails of" the family Val- vatidae {V. bicar'mata and V. tricariiiata) which made tip the sole rep- resentation of grovip II as above defined in the extra-channel zones of the upper lake proper in 1923 both came from very close to the west shore at Rome, and so can not be regarded as standing for any ver\- appreciable part of the extensive upper lake wide-waters. A single oc- currence of an unidentified caddis larva was also noted in the haul from the middle of the "Goose Pond", the shallow backwater to the northeast of the upper end of the upper lake which is rather better protected from sewage invasion than the open portions of the main lake, .\gain. in the upper lake channel in 1923 the only two group II species taken were spt- cies of Bryozoa {Phimatclla princcps, two varieties) which attach them- selves to dead shells, and do not live in the mud as do typical bottom species ; and both of these have previously been found in the Illinois River to exhibit a considerable degree of tolerance to pollution if there is some current present. One of them was taken in Spring Bay Narrows only, and the other at Chillicothe*, at both of which places there is much more current than in the lake proper. Analysis of the group II records from the middle lake shows, first of the intermediate zone (stations within first 1500 feet of the mid-channel line), that all occurrences were restricted to the lower third of the lake, and to the westf side of the channel ; and that four out of the total of seven group II species were taken between Long Shore Beach and Al Fresco Park within 50 feet of the west shore. Of the three group II species taken in the outer zone of the middle lake one was taken close to the west shore opposite Mossville ; one 600 feet from the west shore oppo- site the same station; while the third record (of Pliivmtclla princcps. var. friiticosa, a current-loving form), from 1900 feet east of the mid-channel line opposite Al Fresco Park, is most jirobably based on an error— i. e.. mixing of material either in the field, the field laboratory, or at Urbana. The amount found in the bottle was only a trace and could easily have been stuck in the sieve at a neighboring channel station and released at the other without having been noticed. Last, the sole representative of group II from the middle lake channvl (I'ah-ata bicai'i)iatii var. iionncilis) was taken in the middle of the channel in 20 feet of water in the same southwest corner of the lake that housed the great majority of tlie ex- channel representatives of the same group. The principal increases in number of group II species in lower lake cross-sections over 1922 were not in the extra-channel zones, as in the * Includeti as an upper lake station for bettor comparison will) 1922 records. when ChiUicothe was last station north in series. t Stations on tliis side are for the most I'tart closer to the sandy (west) bluff. and are lietter washed at times of flood than the formerly largely hnishy lake areas to the eastward of the steamboat channel. 403 upper and middle lakes, but in the channel itself, where both the fastest and the average current are considerably greater than anything to be met with in either the upi)cr or middle lake, if Spring Bay Narrows and pos- sibly also a short stretch of channel below Al Fresco Park be excepted. Also, when the lower lake collections of 192;} are sejiarated into hauls from the open lake, or lake projier (U. S. Slips and Main Street cross- sections), and hauls from Peoria Narrows, McKinley Bridge, and P. P. U. Bridge—included with lower lake averages, for better comparison with 1922 in some of the tables following—it is found that there were 12 spe- cies of the II group in the swifter water hauls to only one in the hauls made in the wide portion of the lake. This is quite iu line with (he finding of 1922 that about the only cleaner-preference forms that have survived in or re-entered these waters since the mortality of the years shortly pre- ceding 1920, are current-loving forms—as Pleuroceridae among snails; caddis species of the family Hydropsychidae ; and a few sponges and Bryozoa. The comparatively small representation both of group I and group II species in the extra-channel zones of the lower lake proper sug- gests, also, as did the data of 1922, that there continues here some bad effect of wind-blown local pollution. Ptobi.\ L.\kk, 1922-1923 Increase or Decrease in Number of Collections 404 ment in the sanitary condition of the bottom muds. Tabulation shows, however, for the four commoner species in the upper lake and for six in the middle lake almost identical percentages of occurrence in both vears. 405 been possible to distinguish the present and recent sphaeriid snail fauna of the lake and ujjper river as belonging to a distinctly more tolerant grouping than any except possibly one (Cainpcloiiui subsolidinn) of the Illinois River Gastropoda. Illinois River below Peoria, P. P. U. Bridge—Beardstown, 71.5 Miles Some imjM'ovement is indicated as we ))rocccd down the river from Peoria, it appears, both by the lessening variety and abundance of the tubilicid worms and the more ])ollutioiTal midge larvae; tables, pp 407-408. The large decreases in the total of group I—polliilional and more or less tolerant species—from 34-35 kinds in Peoria Lake to just over a dozen kinds in the two reaches of river recognized above and below Havana, do not, however, mean at all what a first glance at the figures might indicate. The far greater ])ortion of the decrease in the number of group I species is in fact due to the dropping out below Peoria Lake of most of the less tolerant S])haeriid snails and Chironomidae ; a matter without doubt due largely t(j the lesser suitability of the generally harder mud or sand and shell bottom of the river in these sections (if we excejjt the first S miles above Hanava ) than to any other cause; the species of Pisidium and Sphaerium, in particular, which have persisted through the recent pollution in Peoria Lake, never having been found either in variety or numbers in the river between Peoria and Beardstown in the past fomleen years of collecting. So far as the'grou]) II or cleaner-i)reference species are concerned, again, instead of increasing down stream below Peoria as the grou]> I kinds decrease, as we would expect if the latter indicated im]irovement, they also fall oflf rapidly in variety as we proceed south, though, it is to be noted, along with a rather marked decrease also in the number of col- lections ; table, \>. UKi. The greatest variety of grouji II kinds in the three' reaches recognized below Peoria Lake was taken in \.\\^ somewhat more than 20 miles between Wesley and the Copperas Creek Dam, where IS group II species were taken in \\yi'A in 21 collections, comjjaring with 20 in Peoria Lake from 75 collections the same season. Here there is for the most ]iart good current, and princii)ally harder bottom than in Peoria Lake, both of which indicate reduced sedimentation, which seems to pro- tect a good many current-loving organisms, such as Planaria, Bryozoa of .several kinds, the larvae of certain Trichojjtera (caddis-flies), and others, which might otherwise succumb in the face of the new load of Peoria and Pekin ))oilution. Between the inouth of the S])ring Lake Canal, shortly below Copperas Creek Dam, and Havana, the number of cleaner-prefer- ence s|)ecies taken dio]iped to only twelve kinds in the total of nine collec- tions taken; a number perhajis not unduly small, in view both of the con- dition of the mud and the small number f)f collections; though it is recalled that this was by all odds the richest section along the whole Illinois River some ten years ago, at which time it yielded nearly seventy kinds of small • 406 bottom animals, practically all of common occurrence at some stations in the range, which have since then disapiieared from collections altogether; pp. 413 and 419. Here, in the first eight miles aljove the Spoon River bar, at Havana, sedimentation is especially active at times of floQd reces- sion, finally depositing on the bottom a gOodly portion of the load of more or less putrescible svispended solids that mostly passed over the heads of the bottom animals in the reaches between Liverpool and Peoria. Below Havana, in the thirty odd miles to Beardstown, in the summer of 1023 only six group n species were found in a total of thirteen bottom hauls taken. This section of the Illinois, was, however, rather noticeably ]Kior in bot- tom species at most of the stations worked in the seasons of collecting be- tween 1913 and 1915 ; though even our lists from it show a total of fully two dozen kinds of small bottom animals that have failed altogether to appear in collections made since and including 19"30. Decrf.\sk of Both Grovp I and Groii' II* Spbcies FKOM Pkori.v Lake Southward, 1923 407 Total TtuiKuiDAK and T. tubifex Taken Above Pex)ria, 1923* Average Nos. per Sq. Yd. 408 Total Tiiukicidak am) T. iiniiKX Takkx Below PEoitfA. 1923* AVT.RAGE NOS. I'KK S(J. Yl). Total Tubificidae Channel 409 is noted, on the other hand, in the Hniited reach of around nineteen miles between the Spring Lake Canal and Havana, .where in 192;) twelve cleaner-preference forms were taken in nine dredge hauls compared with only two in fourteen hauls in 1920, a finding that would seem at least on its face to indicate some improvement in the condition of the muds in the three years. The number of group II species taken below- Havana was, however, only half as many in 1923 as in 1920, in a mileage considerablv greater, though with the number of collections less, run- ning to a total of only six species in thirteen collections covering thirty miles of river length in 1923, compared with twelve kinds in twenty-two collections from about 19 miles of river in the summer three years before. As already mentioned, the section of more or less shifting sand or sand and shell to hard bottom between Havana and Reardstown was known before the recent mortality for the sparseness and irregularity of distribution of its small bottom poi)ulation ; and because of this and the factors favorable to error that lie back of it, less importance is prob- ably to be attached to such variations in numbers than in sections where the bottom-dwelling organisms—chiefly mud bottom forms in the Illinois River—have a more suitable and more stable substratum on wdiich to live. A better test of the changes that have taken place in recent years in this and other sections of the Illinois River, inclusive of Peoria Lake, because it concerns both larger numbers and greater and therefore more convincing contrasts, consists in g'jing farther back, to the period 1913-1915. comparing our recent species lists with those of that time, and noting the absentee names of the old fauna, side by side with recent survivals and new entrants. 410 Changes in Number of Group II (cleaner preference) Species betwekn 1920 and 1923 all zones combined 411 •greater emphasis on the area embraced under the head of Peoria Lake, which, inclusive of ChilHcothe and the P. P. U. Bridge, amounts to an even twenty miles; and where 181 of the total number of 260 hauls were made. In the three short reaches recognized below Peoria collections ran only 27, 23, and 35, compared with 50, 55, and 59 in the same sections in the period 1913-1915. In both periods there was an essen- tially similar distribution of collections as between channel and shore, or shallower water zones ; with the dift'erence, itself apparently attribut- able to the same influence that destroyed the bottom organisms, that more vegetation was encountered at the shallower stations in the earlier than in the more recent collecting. In making the comparisons many of the more distinctly weed-forms have been thrown out entirely, .though some species of both periods that live a part of the time in the bottom and a part on vegetation are necessarily included. To equalize matters further, some of the 1913-1915 material that had been earlier rather incompletely determined for a mass-valuation calculation, was gone over again in 1923 for additional species, at the expense of several weeks' time. The results of the comparisons are shown in the table on page 413, following. Briefly, the figures show around a dozen kinds of formerly common cleaner-preference species of small bottom animals that have disappeared from Peoria Lake in ten years ; a similar number for the twenty odd miles between Peoria and the Copperas Creek Dam ; nearly seventy kinds that have recently failed to appear in the first ten to nine- teen miles above Havana ; and twenty-four or more kinds that are miss- ing in the more than thirty miles between Havana and Beardstown. These numbers include no fresh-water mussels except a very few scat- tering occurrences of very young or dwarf individuals, taken with the mud dipper, small Blake dredge, or Petersen dredge ; and would be very much larger, particularly in Peoria Lake, had it been possible recently to cover the area thoroughly with a commercial mussel bar, for com- parison with Danglade's 1911-1912* lists of nuissels from the Illinois River. Despite the inequalities and deficiencies mentioned, the results of the comparisons seem for the most part understandable, as they are con- sistent with each other and with otherwise ascertained facts of the biology and hydrography. First, with regard to the relatively enormous losses of cleaner-preference species in the formerly exceedingly rich reach of river just above Havana: Here is where the bottom fauna formerly had both its greatest variety and its greatest abundance ; favored both by the slacker current above the Havana or Spoon River bar and the rich soft mud bottom resulting therefrom. Here also because of the same factor of more abundant sedimentation was where the more sensi- tive bottom organisms might be expected to be put in the greatest jeopardy as the stability of the suspended matters carried this far down the river became lessened. • Report. U. S. Bureau of Fl.xherles. 1913. 412 The notably small size of the list of missing species of the old 1913- 1915 fauna of Peoria Lake, on the other hand, particularly when it is considered that the number of collections taken in the earlier period. 46 in all, was more than four-fifths as many as supplied the abundantly varied species lists from the reach Liverpool-Havana, seems at first prac- tically unexplainable unless we assume that Peoria Lake had already been injured by the sewage of Chicago and up-river towns still earlier than that time. Conspicuous among the missing forms in Peoria Lake collections in 1913-1015 were various aquatic insects, particularly those belonging to groups other than the Diptera: as Odonata, Hemiptera. Neuroptera, and Coleoptera. Though the shallower areas at that time were abundantly su]3plied with aquatic plants it was noticed that results even of "weed tank" collecting were extremely poor, also, as compared with results obtained in the same way in the shallow lakes at Havana. But though aquatic insects other than Chironomidae were rare, the rela- tively sensitive Viviparidae and Amnicolidac, that have since disappeared as far south as Beardstown, were still holding on. though not in nearly as great numbers as near Havana. And as late as 1912-1914 Danglade in work for the U. S. Fisheries Bureau found more than forty kinds of mussels between Chillicothe and Peoria Lake, of which twenty kinds were counted in the piles picked over at Chillicothe. Evidently, if there was any injury previously to 1913-1915 it must have been principally in the wide waters—the mussels are for the most part of the channel or near it—and would point to certain groups of aquatic insects as even more sensitive than the recently exterminated Gastropoda. Of the "missing" lists from the reaches distinguished below Peoria Lake it may be noted that the first one, that between Wesley and the Copperas Creek Dam, was very probably quite as early as 1913-1915 in- fluenced somewhat unfavorably by the heavy load of Peoria and Pekin wastes ; as well as by the limiting influences on the variety of small bottom animals of the swifter current and harder bottoiy. Li the latter respect the section of river between Havana and Beardstown was simi- lar, to a large though not to ([uite so great an extent, perhaps, if the slack water pool above the mouth of the Sangamon be taken into account. That, and the greater distance from the Peoria and Pekin drains, favored a somewhat greater variety of cleaner-preference forms ten years ago than we could have expected between Peoria and the Copperas Creek Dam ; though far from that which seemed to develop so easily in the lake- like section of ten or so miles just above Havana. 413 Number of Species* of Small Botto.m Am.m.^ls i.\ 1923 Collections Compabed WITH Ni-MiiEB Missing in S.vme CoLLraxio.Ns o.x Basis of 1913-1915 Recobds Alt. Zones Co-Miilnkii 414 Total Numbers of Group II, or CLEAXiai-PREFEEENCE Species. Compared avitii Total Number of Collections. 1920-1923 415 • 2. Leeches (Hirudinea). At least four or five species, including ai)parently, Erfyobdclla punc- tata (Leidy). and two species of Melobdella : taken in all zones of the river and lake, from Lacon southward, 1!l"^;!. The sjjccies of Er]i()hdel]a mentioned was definitely associated with ijollution in W'eston and Turner's studies of the Coweeset River in 1!»11. 3. Midge Larvae of pollutional habit. (Chironomidae) Chironomus pUimosus Linnaeus, var. Chironotnus decants Johannsen Cliiroiioimis lobifcnis Say Several undetermined Cliironominac and Tanypinae, like the three species of Chironomus preceding, with range from Chilli- cothe or head of upper Peoria Lake, south. 4. Other Chironomidae, witli distribution for most part from middle or lower Peoria Lake southward. Chirononiiis digitatus Malloch Cricotopus species Orthocladius Palpoiiiyia spp., probably two. Forcipoinyia species Procladiits species Tallypus species Unidentified Chironominae and Tanypinae, several species. It is quite possible that some of these imperfectly determined forms are in reality species with distinct preference for clean bottom ; but occur- rence in Peoria Lake, even in the outer zones, in its recent condition, may be taken to indicate rather more than the degree of tolerance shown by the more sensitive species of that description. 5. Sphaeriid Snail of especially tolerant habit. MitscuUum transvasum Say. This species was found associated with sludge worms of the genera Limnodrilus and Tubifex, where there was almost complete oxvgen exlmustion one foot from bottom, both in 1020 and 1922. 6. Sphaeriid Snails of less tolerant* habit. MuscuUum truncatmn Linsley Pisidium coniprcssum Prime Pisidiuiii coin planat urn Sterki Pisidium paupcrculum var. ciystalcnse Sterki Pisidium species Sphacrium staiiiinciim Conrad Sphacrium striatiuum Lamarck Sphacrium striatiuum var. lilycashcnsc Baker Sphacrium species • The distribution of this subdivision of group I. ami reasons for their distinc- tion in degree of tolerance from other Illinois River snails. Is discussed In detail In the 1922 paper on Peoria Lake. 41G 7. Viviparid Snail of unusual tolerance. Campeloma suhsolidmn Anthony. This species was taken in upper Peoria Lake in 1922 ; and in the river as far north as Starved Rock in 1912, which was at that time sHghtly above the lower limit of the Sohaerotikis zone. Group II CLEANER PREFERENCE SPECIES; BUT SEE QUALIFICATIONS BELOW Though these species are clearly to be grouped as cleaner-preference • forms by comparison with those included in Group I preceding, as com- pared with the assemblage of species wholly exterminated in Peoria Lake and the Illinois River to a point below Havana shortly before 1920 even they may be judged to possess a measurable, if rather slight, degree of tolerance. They are for the most part, both in Peoria Lake and elsewhere, however, confined either to locations very near shore; to the swifter water sections, as the narrows of the lake, or shortly below dams; or to the southwest comer of middle Peoria Lake, just above Peoria Narrows (see p. 17, and foot-note thereto). 1. Mussels (Unionidae) Lampsllis pawns Barnes. S. W. portion of middle lake and Peoria Narrows. Lampsilis gracilis Barnes, young. Wesley, shore-zone in good current. Lampsilis species, young. Wesley and Seven Mile Island, in current. Plaqiola donaciformis Lea. Quiver Beach, more probably from the lake than the river hauls. Label does not distinguish. 2. Snails. (Valvatidae and Pleuroceridae) Valvata bicarinata Lea. W. beach, Rome. Valvata tricarinata (Say). W. beach,' Rome: also taken in same location summer 1922. Valvata bicarinata var. normalis \\'alker. Shore zone, Mossville ; channe, Al Fresco Parkl Gouiobasis livcsccns Mcnke. Channel. Peoria Narrows and McKinley Bridge, in strong current. Plciiroccra clcvatum var. Ici^^isii. Channel, Peoria Narrows, Mc- Kinley Bridge, and Pckin, in strong current. 3. Sponges (Porifera) One or more species taken. Channel at Peoria Xerrows and Pekin, in strong current. 4. Fresh-water Hydroids. (Hydrozoa) Cordxlophora lacuslris .Mlman. Kingston Ferry near shore. 417 5. Planarian Worms. (Turbellaria) Several unidentified species. Common in the channel from Spring Bay south ; and in outer zones from P. P. U. Bridge south. 6. Crustaceans. ( Amphipoda and Isopoda) Hyalclla knickcrbockcri Bate. Channel from Peoria Narrows south ; outer zone, as far north, once, as below dam at Henry. AscUus intcnncdiiis Forbes. Channel, Kingston Ferry. 7. *Moss Animals. (Bryozoa) Plimiatclla f^riiiccf's Kraejielin. var. fniticosa. From Chilli- cothe south, in the channel ; was noted to be especially toler- ' ant, also, in the up])er river in 1911-1912, at that time occur- ring as far north as Starved Rock, but incorrectly named. A recorded occurrence in V.i'i'3 in the outer zone opposite .\1 Fresco Park is probably an error, as the organism rerjuires good current unless conditions are otherwise excellent. Plimiatclla priiiccf's Kraepelin, var. iiiiicosa-sf^oiu/iosii. Chan- nel, Peoria Narrows south. PUtmatella polymovpha Kraejielin, var. repots. Channel. Wes- ley south, in current. Paludicella ehrcnbergii van Benden. Channel, McKinley Bridge south, in good current ; outer zone. Seven Mile Is- land and Kingston and south. VrnatcUa gracilis Leidy. Channel at McKinley Bridge and Pekin, in strong current. 8. Caddis-fly Larvae. ( Trichoptera ) Hxdropsychc species. Channel. Peoria Narrows south, in cur- rent ; outer zone at foot of Grand Island. Polyccntropus species. Channel, Copperas Creek below dam and south, in current. Molaiiiia species. Near shore. Quiver Beach. Probably a lake collection, as this is a sand beach form. Unidentified species. Unknown current-loving form at McKin- ley Bridge in channel, and south ; one or two stagnant-water . species, with basket-shaped cases, in outer zones from Rome south. 9. .May-fly Nymphs (Ephemerida) Hcxageitia bilitieata Say, Channel at Havana and at hi;id of Hickory Island : near shore, once at Pekin a\u\ once each at foot of Grand I.^land and head of Hickory Island. • I think a better common name would be soft-w;ined or frish-watir ci.ral; a.«! the group wa.s originally includiil with the iiiarin<- inralH by Klirenberi; about a hundred years ago. 418 10. Dragon-fly Nymphs (Odonata) Ischmira species. Channel, McKinley Bridge, in strong current. Goniphits plagiatus Selys. Channel at Liverpool. Goniphus species. Near shore at Kingston Ferry. 11. Orl-fly Larvae (Neuropteraj Sialis infumata Newman. Near shore, S. W. end lower Peoria Lake. Pre-1920 Bottom Species* Recently Missing from Illinois River and Peoria Lake Dredge Hauls From Species Lists of 1913-1915, REFERRED TO AS GrOI'P III IN PRECEDING T.\BLES 1. lllhw'is River and Peoria Lake, Chillicothe to P. P. U. Bridge, inclusii'e. Tzvche species; 46 collections; all zones couibined. Mollusca Viviparidae Fivipara conteetoidcs W. G. Binney Vivipara subpurpurea Say Lioplax subcarlnatus (Say) Amnicolidae A>nnicola einarginafa Kiister Amnicola liniosa (Say) Somatogynts siibglobosus (Saj') Ancylidae Ancylus species Insects Ephemerida Hexagenia bilineata Say Callibactis species Caenis species Diptera Chironoinus tentans Fabricius Chironomus nigricans Johannsen 2. Illinois Ri^rr, Pekin to Copperas Creek Daw. inclusive. Thirteen species; 30 collections; all cones combined. ^lolhisca LTnionidae Anodonta iinbecillis Say • No mus.sols included except very young indi\'it1ualR or dwarf species: i. e.. tliose talten witii mud dipper or small iron dredije. 419 Viviparidac Vivipara contcctoidcs W. G. Biniiey Fivipara suhpurpurca Say Lioplax subcariiiatus (Say) Canipcloiiia sitbsoliiiiiin Anthony Pleuroceridae Goniobasis livcscciis Menke Ancylidae A lieylus species Aninicolidae Aiiinicola cmarginata Kiister Amnicola lustrica Pilsbry Valvatidae Valvata tricarinata (Say) Planorbidae Planorbis parvus Say Fori fera Unidentified fresh-water sponges, at least one species. Crustacea Isopoda Ascllus iufcniicdius Forbes 3. Illinuis River, Liverpool to Havana inelusive. Sixt\- nine species; 55 collections; all cones combined. Mollusca Unionidae Anodonta corpulenta Cooper. Young Anodonta iinbecillis Say Lainpsilis lutenlus (Lamarck). Young Laiiipsilis fallaciosus Simpson, Young Lampsilis parvus Barnes Plagiola donaciformis Lea Sphaeriidae Sphacriuni stainineuui Conrad Sphaeriuut striatinuni Lamarck Spliaeriuni simile Say Viviparidac Vivipara conteetoides W. G. Binney Vivipara subpurpurea Say Campeloma dccisum Say Lioplax subcarinatus (Say) Pleuroceridae Goniobasis livescens Menke Pleurocera clevotum, var. lewisii Lea Amnicolidac Soniatofjynis subglobosus (Say) 420 « Amnicola cincinnatiensis (Anthony) Ainnicola limosa (Say) Amnicola lustrica Pilsbry Valvatidae Valvata tricarinata Lea Valvala bicarinata (Say) Physidae Apparently at least two species Planorbidae Planorbis parvus Say Planorb'is trivolvis Say Planorbis exacutiis Say Lymnaeidae Lyinnaca fminilis Say Lymnaea paliistris (Muller) Ancylidae Ancylits species Porifera Unidentified fresh-water sponges, at least 3 kinds Hirudinea Apparently at least 3 species of leeches not re- cently taken. Crustacea Palaemonidae Palacmonctcs c.rilipes Stimpson Insects Ephemerida Callibactis species Caenis species Hcxagcnia bilincata Say Hcplagcnia species Odonata Calopteryx species Unidentified Agrionidae, at least two species. Mcsothonis simplicicoUis Say Epicorditlia princcps Hagen Heniiptera Corixa burmcislcri Ficber Corixa species Notoiiccfa species Zaitlia Huminca (Say) Neuroptcra Sialis infnmata Newman Corydalis species Trichoptcra Rhyacophila species 4-n Polycentropus species Coleoptera BcrosHs species Tropistcniiis species Pcltodytcs species StcncUuis species Unidentified parnid, etc., at least two species. Diptera Chiroiiotnns teutons Fabricius Chiroiiomus viridicollis v. d. \^^ulp Chironomus fcrnigincoviltatus Zetterstedt CliiroHomiis inodcstjis Say Cricotopiis trifasciatiis Panzer Corcthra punctipcniiis Say Sepedon species Odontomyia species Unidentified tabanid Psychoda species 4. Illinois River. Matanzas to Bcardstown, inclusive. Twenty-five species; 59 collections; all zones com- bined Mollusca Unionidae Strophitns edentulus (Say). Young Plagiola clegaus Lea. Young Anodonta imhccillis Say Viviparidae Vivipara contectoides W. G. Binney Vivipara sitbpurptirca Say Lioplax subcarinatus Say Pleuroceridae Plenrocera elevatum, var. Ictvisii Lea Goniobasis livescens Menke Anmicolidae Amnicola emarginafa Kiister S'oinatogynis snbglobosus (Say) Pbysidae Apparently at least two species. Ancylidae Ancylus species Hirudinea At least two species of leeches not recently taken. Insects Ephemerida Hexaqenia bilincata Say 422 Hcptagcnia species Coleoptera Stcnclmis species Diptera Tanypus monilis Linnaeus Palpomyia longipcnnis Loew Chironoinus dux Johannsen Chirouoiiuis fcrrugbicovittatus Zetterstedt Chironomus tcntans Fabricius Cricotopus trifaciatus Panzer Procladius concinnns Coquillett