BTJLLETIISr
OF THE

ILLINOIS MUSEUM OF NATURAL HISTORY.

LIST OF ILLINOIS CRUSTACEA,
WITH DESCRIPTIONS OF NEW SPECIES.

By S. A. FORBES.

The following list is to be regarded as only a first contribution to the

knowledge of our Crustacea, as it presents the results of a single season's

work. Considering the fact that, while our streams and pools are populous

with interesting forms, many of which are new, only a single species outside

the genus Cambarus has heretofore been credited to the state, it is hoped
that even so imperfect a paper as this may not be without its uses.

I wish to acknowledge especial obligations to Professors A. E. Verrill

and 8. I. Smith of Yale College for specimens and for suggestions concern-

ing the species of Eubranchlpus and Crangonyx described herein, and to

the latter of these gentlemen for many other favors.

Cambarus acutus, Gir. Very common in central Illinois. Taken in

large numbers at Normal and Pekin. Of '25 males examined, the first ab-

dominal legs were all those of Hagen's variety A. In none was the epistoma

pointed, and a distinct lateral thoracic spine was present in but one. In

twenty of the specimens the margins of the rostrum were distinctly convex
from the base to the apical teeth ; and the latter were in all much smaller

than in Hagen's figures, the distance across the teeth being but one-fourth

to one-third that across the base of the rostrum between the tips of the

spurs. The tubercle in the basal foveola was elongated, notched in front

and continued backward into a very slight cephalo-thoracic carina. Be-
tween the posterior callosities and the transverse line, the cephalo-thorax

was finely rugulose. The females observed were also variety A.

C. stj/ffius, Bundij. " Male. Rostrum long, triangular, smooth above,

small teeth near apex, foveolate at base ; carinoe parallel, separated from base

of rostrum by slight grooves; cephalo-thorax somewhat compressed, smooth

or slightly punctate above, granulate on sides, areola narrow, smooth

;



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antennal plates wide, truncate at apex, apical teeth short ; epistoma rounded

in front, twice as wide as long ;
third niaxillipedes hairy on inner sides, hands

short, smooth above, serrate on inner margin, fingers short, straight, rib-

bed and punctate above, contiguous margins tuberculate, outer one hairy
;

third and fourth joints of third thoracic legs hooked ;
first abdominal legs

short, truncate, enlarged towards apex, apical part recurved, then ending

in three obtuse points turning outward, leaving a wide groove passing up on

outer side behind teeth. The female has ventral ring flat, with posterior

margin slightly elevated. Lake Michigan ; washed up during a violent

storm." {W. T. Bundy.)

C. troglodytes, Lee. This species I have not yet taken. It is men-

tioned here on the authority of Dr. Hagen.

C' virilis, Hagen. A few specimens have been collected at Normal,

Cairo and Pekin, Ills., all young or of the second form except one male

from Normal, which belongs to Hagen's variety A. The thorax is, how-

ever, broader and smoother, and the areola wider than in the typical form,

which has been received from Rock river, Wis.

G. wiaconsmensis, Bundy. " Male. Rostrum wide, narrower in front,

straight, nearly plane above, foveolate at base, anterior teeth small, acumen

short, acute ; cephalo-thorax cylindrical, punctate, anterior margin not an-

gulated, lateral tooth obtuse ; dorsal area rather narrow, indistinctly defined
;

antennal plates longer than rostrum, greatest width in apical half; antennae

slender, reaching to middle of abdomen ; epistoma as wide as long, truncate

in front ; maxillipedes hairy on inner side and below at base ; third joint of

third legs hooked ; first abdominal legs long, bifid, nearly straight, exterior

part longer, tips slightly recurved ; tips of interior parts recurved, acute,

swollen near apex. Normal, 111., and Racine, Wis.." ( W. T. Bundy.)

C. placidus, Hagen. " Quincy, 111.," (Hagen.) I have not seen this

species.

0. propinquns, Gir. Not common. Taken at Normal, Pekin and

Freeport.

C. immmiis, Hagen. This is the commonest species of central Illi-

nois. It is especially frequent in the muddy ponds of the prairies, whence

it may be drawn by the hundred with a small seine.

The general form of the rostrum of the young is the same as that of

the adult ; but more or less evident ante-apical teeth are present. The
abdominal legs of the second form of the male are much thicker at the tip.

In the first form the branches are slender and distinct throughout the distal

half of their length, the outer branch is compressed at tip, and the inner

depressed and widened a little, and channeled on the anterior surface. In

the second form both branches are equally thick and strong, neither is com-
pressed or channeled, and the two do not separate except at their tips after

making the backward turn. The sudden thickening of the leg at its posterior

middle is much less evident in the second form.

About one-fourth or one-half the specimens taken from stagnant

ponds in midsummer are more or less completely covered above by the eggs

of a species of Curixa,—probably C. alternata, JSay, since this is much the



commoner of the two species found in such situations, the other being as

yet undescribed.*

These eggs are attached as closely as they can be placed, by the end
opposite the micropyle, and do not seem especially to inconvenience their

bearers.

The point of attachment preferred is the margin of the abdomen, out of

the way of the legs : but the eggs are gradually extended along the sides of

the cephalo-thorax until sometimes the body is almost entirely covered. A
careful search of the weeds and other submerged objects in the ponds dis-

covered no other place of deposit of these eggs. As these ponds usually go

dry during the summer, it seems not unlikely that the Corixa inay attach its

eggs to the crawfish in order that the latter may, in such an event, carry

them to other waters. It is not to be supposed, however, that the Co-
rixa is entirely dependent on the crawfish for the preservation of its progeny,

for the parent can fly, and is occasionally taken on the wing; nevertheless,

this curious expedient must prevent a great waste of eggs, and so operate to

the advantage of the species. But the subject requires further study.

(J. obcsus, Ha<jen. Very common. The largest in the state.

6'. gracili!', Bunclt/.* "Rostrum short, wide, depressed, concave above,

acumen short ; cephalo-thorax compressed, areola none, the pleura meeting

on median line of dorsum, posterior spatium much wider than anterior

;

chelae long ;
inner margin tuberculate-serrate, fingers slender toward apex,

outer one with strong tubercle on inner margin near base, movable finger

with strong tubercle near middle of inner margin ; carpus long, strongly

toothed on inner, and lower front margins
;
third maxillipedes hairy on in-

ner sides
;
third joint of third thoracic legs hooked ; first abdominal legs of

male truncate, with several small apical teeth, of which the inner one is

much longest, slender and pointed outward, base of these legs inserted in

deep sinuses in the strongly developed ventral part of first abdominal seg-

ment. Ventral ring of female movable ; longitudinal fissure widest be-

hind." ( W. T. Bundy.') Very common along water courses in early spring.

It was first detected by Prof. Bundy, in the museum collections, in the au-

tumn of 1875, has since been taken in great numbers at Normal, and has

been received by Prof. Bundy, from Racine, Wis.

Palaemon ohioni!-; >Sniith. Abundant at Cairo, where it is frequently

eaten. Smaller specimens were taken in the Mississippi near Grand Tower,

in Jackson county, and it is reported by boatmen to occur from St. Louis

to New Orleans, growing larger towards the south. It has not yet been

found in the Illinois River.

Palaemonek's exilipes, Stimp. Very common in the Illinois River,

where it seems to be the only shrimp. Taken in large numbers at Pekin.

Hyalella dentata, Smith. Occurs in myriads in the swamps of the Cal-

umet river, at South Chicago, and sparingly in Rock river, at Oregon,

Ogle county. Not seen further south.

*Uhler.
*The descriptions quoted have been kindly furnished me by the discoverer of the

species.



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Gammariis fasciatus, Say. Apparently occurs throughout the state,

in small rocky streams. Collected at Deer Park, La Salle county, in a

small branch of the Vermilion, and in several streams in Jackson and Union
counties. Scores of males and females were taken together under stones, on

the 30th of July.

In specimens from southern Illinois, the hands of the first pair in both

sexes bear stout spines on the distal half of the posterior margin in addition

to those on palm and at the tip of dactyl. A short transverse row of long

hairs is situated at the base of the median palmar spine. The inner side of

the hand of the second pair in the male is ornamented with two longitudinal

series of short transverse rows of hairs,—the posterior of five rows, the an-

terior of three. The palmar margin in the female has the lamellar edge.

The lateral clusters of spines on the fourth posterior abdominal segment, in

both sexes, each contain one very stout spine and several slender ones,

while the median cluster consists of slender spines only. Each of the clus-

ters on the fifth and sixth segments consists of two stout spines and several

slender ones, except the median fascicle of the sixth segment, which consists

of two distinct clusters of slender spines. The divisions of the telson have

two clusters of hairs on the upper surface near the outer margin, of which

the basal contains two spines. The spiny tips of the divisions are emarginate.

Crangonyx gracilis, Smith. Very common in central Illinois. Col-

lected at Bloomington, from slow,shallow streams. These specimens differed

in several small details from those described by Prof. Smith, the most im-

portant relating to the caudal stylets. In the typical form the tips of the

three pairs are even ; but in the Bloomington specimens the second pair

extends farther back than the third, and the first farther than the second.

The inner ramus of the last pair is sometimes unarmed, but oftener bears

one or two spines at or near the tip. The length of ovigerous females is

10 mm. ; of the largest males observed 85 mm.
A form from southern Illinois represented in my collections by a few

females, I cannot distinguish specifically from the above, although the second
hands are proportionally longer and narrower and much more spiny, the

anterior and posterior margins less convex, and the palmar margin more so.

The tips of the caudal stylets reach the same perpendicular plane, and the

inner ramus of the last is always as long as the width of the outer and bears

one or two spines.

Crangonyx murronatus, Forbes. This remarkable species is perhaps

entitled to rank as the type of a new genus ; but, until I have the material

for a more general study of its relations than I am able to make at present,

I prefer to place it with its nearest allies in the genus Crangonyx.
Colorless, blind ; length 9 to 10 mm, width 1 mm. The head is a

little longer than the first thoracic segment, its anterior margin concave at

the bases of the upper antennae, convex between them ; the posterior mar-
gin straight in the middle and curving forward on the sides. The front

angles of the first thoracic segment are uncovered and produced a little for-

ward ; the hind angles of the first five segments are rounded and produced
strongly backward. The first three abdominal segments have the lateral



(7)

margins and all the angles broadly rounded, and the posterior angles, as well

as the posterior margin of the seventh epinieron, are slightly notched and
bristled. The xipper antennee of the male are two-thirds to four-fifths as

long as the body. The first and second joints of the pedicel are sub-equal,

each about as long as the four basal joints of the flagellum ; the third is

one-third as long as the second. The flagellum is about five times the

length of the pedicel, and is composed of 30 to 35 joints, each with a few
short hairs at tip, and all except the seven or eight basal joints and the last

with a slender olfactory club. The secondary flagellum contains two bristled

joints, together a little longer than the first of the primary flagellum. Ped-
icel oi hirer nntenn?c. longer than that of upper, the last two joints equal,
each a little longer than basal joints of upper antenna. Flagellum nine or
ten jointed, without olfactory clubs. Right mandible with dental laminae
equal, each with five conical, obtuse, sub-equal teeth. The anterior lamina
of the left mandible is much the larger and stronger, with three very strong,

blunt teeth : posterior lamina with three slender and acute teeth. Palpus
three-jointed ; basal quadrate, about half as long as second, which is clavate
and nearly twice as wide as long, with about ten long hairs on its rounded
hind margin which are longest and closest distal ly. Last joint a little

longer and narrower than second, regularly convex in front, straight on
proximal half of hind margin, slightly concave on distal half, and fringed
here with about 24 slender hairs, the three or four at tip becoming suddenly
very much longer. A few scattered hairs on front margin of this joint.

Inner plate of anterior maxiUa is nearly hemispherical, about half as

long as outer, with four plumose hairs on the rounded margin, which are
about as long as the plate itself. Palpus two-jointed, first quadrate, one-
third as long as second, which is oval, pointed, tipped with two claws and
some smaller spines. Laminae of basal joints of maxillipeds short, neither
pair extending beyond tips of succeeding joints.

First tioo pairs offeet equal. Dactyl of first pair in male curved, two-
thirds as long as hand. The latter is broad-ovate, two-thirds as wide as

long, the palmar and posterior margins forming a wide angle. Long hairs

on posterior surface in transverse rows. Palm with about fifteen short,

notched spines, each with a hair arising from the notch. Carpus sub-tri-

angular, three-fourths as wide as propodus, hind margin very short, with
one or two pectinate spines and a few long hairs. Second pair similar, pro-
podus a little longer and narrower : carpus as wide as propodus, posterior
margin longer, with about five transverse rows of long bristles, of which the
distal row are doubly pectinate on terminal third. The three posterior
pairs of thoracic legs increase in size backwards, the first of these being not
quite two-thirds as long as the last. The seventh epimeron is narrow, with
the lower margin regularly arcuate. The tips of the first pair of «?ia7 Ze^.s

extend beyond the tips of the second, and these beyond the tips of the third.

The latter are therefore very short, about as long as the pedicel of the
second pair. The outer ramus is ovate, truncate, half as long as the pedicel,
and hairy at tip ; the inner is an unarmed rudiment, one-fourth or one-
fifth the length of the outer. The tehon of the male is a smooth cylindrical



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appendage, usually about as long as the first three abdominal segments, and

as large as the last joint of the pedicel of the lower antenna. It presents a

very slight double curve, is obliquely rounded at the end and tipped by a

cluster of short hairs. Tn some cases this appendage is half as long as the

body.

The female differs in the following particulars. The upper antennae

are only about half the length of the body, the flagellum not more than

three times as long as the pedicel, and the secondary flagellum is usually a

little shorter. The propodus of the Jirst pair offeet is similar in outline, but

the palmar margin and dactyl are shorter and the posterior margin longer.

The second pair are extremely like the second of the male, but are decidedly

smaller than the fii'st. The telson affords a difference so remarkable that

the two sexes, at first sight, would hardly be referred to the same genus.

In the female this is very similar to the telson of 6'. f/racilii^, Sm. It is

flattened and slightly emarginate, a little longer than broad, extending to

the tips of the second pair of anal legs, and bears two terminal clusters of

spines of four or five each.

This species was first discovered by me in a well at Normal, 111., during

the summer of 1875. It was subsequently found by Mr. Harry Glarman in

great numbers in springs, and even at the mouths of drains, after a long pe-

riod of heavy rains. With the advent of dry weather it entirely disappeared

from these, but still occurs sparingly in wells.

Asellus hrevicanda, Forhes. Length without caudal stylets, 10 mm.
to 15 mm.; width, 3 mm. to 5 mm. Color as in A communis. Head a little

longer than first thoracic segment and about two-thirds as wide ; anterior

margin distinctly concave in middle and retreating each side, anterior angles

distinct, sides straight, nearly parallel on anterior three-fourths.

The posterior fourth is produced on each side into a prominent lateral

lobe bearing several stout spines. The distance to which this lobe projects

equals half the length of the lateral margin of the head in front of it. The
eyes are rather small but prominent, and are situated just within the middle

of the straight portion of the lateral margin. The re-entering angle at the

side of the head is a little less than a right angle, but its apex is rounded.

The thoracic segments are sub-equal in length, of the usual shape, but be-

coming very concave behind. The concavity of the last segment amounts
to more than half the length of the segment. The anterior angles of the

first segment are deeply emarginate, the notch being nearly filled by the

epimeron ; but there are no other lateral emarginations in any of the seg-

ments, nor are any other epimera visible from above. In some young speci-

mens the lateral margins of the two or three posterior thoracic segments are

slightly sinuate. The hind angles are all rotmded, and the free margins are

all beset with long bristles, longest on the lateral margins and especially at

the angles.

A short first abdomincd segment is visible in the concavity of the last

thoracic. The last abdominal is wider than long, with a broad rounded
projection occupying the median half or two-thirds of the posterior margin,
reaching half way or more to tips of pedicels of caudal stylets. The pes-



(9 )

terior lateral angles are distinct though obtuse, the hind margin being some-
what concave each side the median lobe ; and the margins are hairy as in

the thorax.

The upper anteiuiae are nearly as long as the pedicel of the lower. The
flagellum consists of 11 to 13 joints, the two terminal together about as

long as the preceding one. The three joints preceding the last bear, each

at its anterior internal angle, a large olfactory club about at long as the

eighth joint of the flagellum.

The loicer nntennae extend backward about to the base of the abdomen.
The last joint of the pedicel is as long as the two preceding. The flagellum

contains about 60 joints in the female and 90 in the male.

The palpus of the ma7idi/jfe is small, three-jointed, the first joint cia-

vate, with three spines on the distal half of the posterior margin and one or

two at tip. The second joint is about twice as long as wide, slightly con-

cave in front and with a distinct median angle behind. There are two or

three scattered haii-s on the basal half of the posterior margin, and many
long plumose hairs, .shortening distally, on the terminal half. The third

joint is ovoid, tapering, very broadly rounded in front and distinctly con-

cave behind. The concave posterior margin bears a row of long plumose
hairs, regularly lengthening toward the tip, and a sub-marginal row of

shorter hairs on the side of the joint. The basal joint oH the pa Ipiis of the

maxUlipe<J is very .short, transverse, about thrice as broad as long, with

outer margin perpendicular to terminal. The second joint is a little broader

than long, rounded slightly without, very broadly within, and plentifully

ciliate on both edges.

The third joint is about two-thirds as long as second, broadly and reg-

ularly rounded within, narrowed about one-third at tip ; the fourth clavate,

incurved, as long as second, at tip about half as wide as long ; the fifth

about half as wide and long as fourth, incurved, obtuse. All the joints bear

long marginal hairs.

The Jivft pair offeet in the male are strongly sub-chelate ; the propodus
a little more than two-thirds as wide as long, the palmar margin straight,

with one strong tooth at base and another at middle. The posterior margin
is only about one-fifth the palmar, and perpendicular to it. The dactyl is

strong, curved, serrate behind with about seven distinct teeth. The terminal

claw is strong, acute and curved. Both margins of the propodus and the

front of the dactyl are hairy : a cluster of longer hairs is seen near base of

claw of dactyl.

The propodus of the female is a little narrower and the palmar margin
is somewhat concave. The tooth at the middle of the palmar margin is

smaller, but quite distinct.

The basal abdominal plate beneath in the female is obtusely triangular,

about half as long as the basal part of the next plate behind. The first pair

of genital plates in the male are long and narrow, the terminal joint truncate,

strongly excurved beyond the middle, and bordered posteriorly by about
six long bristles a third as long as the joint.

In the second pair of plates the basal joint (pedicel) is twice as long as



(10)

tLe rami and three-fifths as wide as long. The second joint of the outer

ramus is ovate and twice the length of the first. The inner ramus reaches

to the middle of this joint, is broader than in A. communis, but of similar

shape, and indistinctly bifid at tip.

The opercular plates do not reach the tip of the abdomen, but are

obliquely truncate, their posterior margins forming a wide re-entering angle.

The anal stylets are very short, flat and broad. The peduncle is ob-tri-

angular, nearly as broad as long, the tip oblique, the inner edge being the

longer and somewhat rounded. The outer ramus is narrow-ovate, obtuse,

as long as the peduncle, and seven-eighths the length of the outer ramus.

This is also ovate and obtuse, the outer margin nearly straight, the inner

convex. All the joints bear many marginal spines, longest at tips of rami.

This species was found in clear, rocky rills in Jackson and Union

counties in Southern Illinois.

Asellus mtermedius, Forbes. This species is more closely allied to A
communis than to A. brevicauda, but, as will be seen from the description^

stands between these two. Its length, in adult females, is but 6 mm., its

breadth about 2 mm. The sides of the head diverge posteriorly, and the

lateral lobe is smaller than in brevicauda, bearing a single spine and a few

short hairs. The first tho7-acic segment is narrowed anteriorly, showing the

epimera, but is not emarginate. The others are distinctly emarginate on

the sides, the eraarginations moving gradually backwards, in the succeeding

segments, from the anterior to the posterior angles. The free margins of

all the segments are strongly spined. The lobe of the hind margin of the

abdomen is shorter and broader than in brevicauda, reaching laterally to the

middle of base of each caudal stylet, and extending backward to the middle

of length of pedicel. The posterior angles of the abdomen are regularly

rounded and indistinct.

The flagellum of the upper antenna is nine-jointed, the first joint short,

about half as long as fourth.

The first pair offeet of the male are stout, the hand two-thirds as wide

as long, the palmar margin straight, with a slender tooth at base and a strong

conical one at middle. The posterior margin of the propodus is very short,

about one-sixth the palmar, the dactyl long and strong, the tip of the claw

when closed reaching beyond the base of the hand. The posterior margin
of the dactyl is serrate with appressed teeth as in brevicauda. The carpus

is triangular, the posterior margin straight and usually armed with a strong

blunt spine at its distal fifth. The hand of the female is narrower

and smaller, its breadth being about half its length. The palm is straight

and shorter than in the male, the posterior margin longer, (nearly half

the palmar), the two margins forming a wide angle. The spine at this

angle is slender, and there is no trace of a tooth on the palmar margin,

or on the carpus.

The first pair of genital plates in the male are short and broad, the

basal joint scarcely longer than wide, the second joint elliptical, broadly

rounded at tip and convex both sides, fringed posteriorly and on pos-

terior half of outer margin by a few short hairs. The pedicel of the



(in

second pair is about as long as wide, the rami arc as long as the

pedicel and sub-equal. The second joint of the outer ramus is ellipti-

cal and thrice as long as the first. The inner ramus is nearly half

as wide as long, the basal processes obtuse and low, the outer one

being almost obsolete. The outer terminal angle is prolonged into an

incurved process, the inner provided with a movable (?) cxcurved claw.

The caudal ati/lets are flat and broad, but narrower than in brevicauda,

about threc-fifth^^ as long as the abdomen. The width of the pedicel is two-

thirds its length. The outer ramus is nearly five-sixths the inner and equal

to pedicel. Both rami are narrow-ovate, and very obtuse, the inner about

four times as long as wide and nearly straight on the outer margin. Both
pedicel and rami are spiny on their ma;-gins, and the latter are tipped with

a few long hairs.

Abundant in the hill-country of southern Illinois, under stones in small

streams.

While these two species of Asellus were found in considerable numbers
on the first day of my trip, I have never seen a specimen of either in the

central or northern part of the state, although I have carefully searched the

most varied situations.

Asellus stycfius, Packard. This species has been peculiarly unfor-

tunate. Described originally from an injured specimen, its structure and

relations were misunderstood and it was made the type of a new genus,

( Caecidotea, Packard). It was soon re-described by Prof. Cope, under the

specific name microcephahis ; and these imperfect descriptions have since

been supplemented by several fragmentary notices in various papers by
Packard and Smith.

With a view to giving a more coherent account of it, 1 have examined
many specimens of both sexes and various ages, and have prepared the fol-

lowing description : A detailed comparison of this species with undoubted

Asellus—especially with the admirable plates of ^-1. aquaticus in the Crusfaces

rf' eau douce de Norvege, has failed to reveal any structural peculiarities

which could possibly serve as the characters of a distinct genus, and I have

therefore united it to Asellus.

Colorless, blind, narrow, very loosed}' articulated, sides nearly parallel,

12 to 14 mm. by 2 to 8 mm.
The head is a little narrower and longer than the first thoracic segment,

narrower in front than behind, with the front margin concave, the front

angles rounded, the hind margin nearly straight. It is a little constricted

behind the mandibles. The fii'st thoracic segment is narrowed a little to the

front so as to show the epimera, the sixth and seventh are also much narrower

before than behind, and longer than the others. The front angles of the

second and third segments are obliquely truncate, the hind angles broadly

rounded. All the segments behind the first arc slightly emarginate on the

sides, the emarginations being carried gradually backward to the posterior

angles. The anterior margins of the segments change gradually from con-

cave to convex, and the posterior margins from sinuate to deeply concave.

The head and all the segments are slightly pubescent above and bor-



I 12 )

dered laterally with short hairs. The large abdominal segment is preceded

by two very short ones. The abdomen is about as long as the last two
thoracic segments, the hind angles rounded bixt distinct, the hind margin

very slightly sinuate.

The dipper antennae reach to the tip of the penultimate joint of the

pedicel of the lower. Pedicel and flagellum about equal, latter ten to

twelve-jointed, bearing a slender olfactory club at tip of each of the four or

five joints preceding the last. Joints of pedicel sub-equal in length, but

the first twice as large as the second.

The lower antennae are about two-thirds as long as the body in the fe-

male, in the male somewhat longer. Pedicel about one-third flagellum,

five-jointed, fifth and sixth joints each longer than the basal three together.

The flagellum contains 75 to 80 joints. The mandibles are almost exactly as

in Asellus aquaticus. The posterior dental plate of the left mandible is

nearly as wide as the anterior. The hairs of the marginal fringe are more
numerous on the right mandible than on the left, and the anterior eight are

toothed instead of plumose.

The mandibular palpus is slender, the basal joint a little shorter than

the second. On the latter the external angulation is considerably behind

the tniddle. The distal joint is narrow, lunate, (distinctly concave on outer

margin) about five-sixths the length of the preceding joint, wnth about 20,

jointed, plumose, marginal hairs, similar to those on the distal half of outer

margin of preceding joint. The two plates composing each mauilla of the

Jirst pair are equal in length. The inner is three-fourths as wide as the

outer, terminating in five plumose hairs. The outer terminates in twelve

strong spines, of which the five outer are stronger and simple, and the seven

inner irregularly and bluntly toothed near their tips. The posterior 'maxillae

as in Asellus aquaticus. The shortcf internal hairs on the two outer plates are

expanded transversely to the plane of the plate and hollowed lengthwise on

the inner face, giving each hair the form of a racing-shell, while both edges

of the hair are coarsely toothed. The basal joint of iho: palpus of the max-
illiped is quadrate, the fourth joint is about as long as the second and third

together. The inner margins of the fourth and fifth are provided with very

long hairs. The flagellum {^fouct, Sars.) is as broad as long, with about

eight scattered hairs at tip and several shorter ones on external margin.

The propodus oi i\\Qfirstpair offeet in the male is very large, broad-oval,

two-thirds as wide as long. A strong curved spine is situated at the proximal

end of the palm, and two truncate, stout teeth separated by a rounded
emargination, near the distal end. The dactyl is strongly curved, es-

pecially at base, its inner edge serrate with six acute teeth appressed towards

tip. The length of the terminal claw is more than one-third that of the en-

tire dactyl. The convex margin of the dactyl bears a few scattered hairs,

and a cluster of four or five near the tip. The carpus is small as in ^.
aquaticus, and spined on its distal margin. The female hand is smaller and
narrower, (width to length as 1 to I4) the palmar margin concave, the pair

of truncate teeth replaced by a single smaller conical one which is some-
times obsolete. The other differences are trivial. The legs become longer



behind, the tip of the second pair reaching as far as the base of the propodus

of the seventh. The abdominal sexual plates of the male are in two pairs,

as usual. (8eo plate). The corresponding plates of the female are but one

pair, rather narrowly ovate, ciliated at tip and on posterior two-thirds of

outer margin, with a few short spines at the base of the inner edge. The

external ramus of the next pair—serving as a gill-cover—bears a terminal

fringe of plumose hairs and a few short spines at base on outer margin. The
inner ramus—first gill —is oblong, two-thirds the length and breadth of the

outer. Both the pedicel and rami of the caudal sti/lets are slender and

cylindrical, the former about as long as the last two joints of the last pair

of legs, the latter tipped each with a cluster of bristles, the inner about

two-thirds as long as the pedicel, the outer varying from one-quarter to two-

thirds the inner. The length of the rami varies greatly with age and sex.

In many old males the inner is very long and the outer minute. There are

four pairs of incubator// lamellae in the female, each pair overlapping by

their rounded inner ends, except the first, which are shorter and have the

anterior internal angles emarginate.

The description has been given above in greater detail than would

otherwise have been necessary, in order to settle the question of genus. The
specic.>- is found quite frequently iu deep wells of central Illinois, in com-

panv with, but much more abundant than, Crangom/x mucronatus.

After a long period of heavy rains during the last summer had greatly

swelled the subterranean streams which these species inhabit, they appeared

at the surface in springs, and even at the mouths of tile drains, in such

numbers that a hundred could be taken in an hour. A few females were

observed with eggs at this time. (July).

Euhranchipus sen-atus, Forbes. This species seems to replace the

E. vernalis, Vrrrill, of the Eastern States, to which it is closely allied. An
important character, constant in the large number of both sexes which I

have examined, is found in the abdominal ser/ments^ which are narrowed in

front, with rounded anterior angles, while the posterior angles are produced

backward, giving a decidedly serrate appearance to the abdominal margin.

The last two abdominal segments are closely united and broader than the

preceding.

Tne antennae extend a little beyond the eyes, and terminate in a cluster

of about five slender olfactory clubs. Tho frontal appendnr/es oi the mdle

are considerably longer than the claspers, to the front inner base of which

they are attached, the line of attachment being parallel to the length of the

basal joint. Their form is irregularly oval, the inner edge being regularly

convex on its distal three-fourths and the outer sinuate—convex on basal

two-thirds, and .slightly concave on terminal third. Both margins are

pectinate, except near base, with thick blunt teeth, which are longest on the

basal half of the outer margin, where they are as long as the undivided part

of the appendage is wide. At the middle of this margin the teeth become sud-

denly shorter. On the inner margin they are longest near the middle, regularly

lessening towards each end. The under (posterior] surface of the appendage,

as well as the teeth, is set with short spines, each springing from an inflated



( 14
)

base. The claspers of the male are shorter and stouter than in E. vernalis.

The basal joint is soft and inflated and bears a corneous rounded tubercle at

its inner base.* The second joint is stout and regularly incurved, strongly

angiilated at its base in front where it is received into the first joint. A
long strong tooth, about half as long as the joint, extends backward and a

little inward from near its base. The rounded tip of this tooth is thickly

set with minute, low, circular elevations, each with a central depression,

within which is a disk-like elevation, the whole having the appearance

of a minute sucking disk. The tip of the clasper is expanded and flat-

tened within so that the inner (anterior) part has a spatulate form,

while the opposite surface rises into a thick prominent ridge, giving to

a transverse section of the tip the form of the letter T. The anal

appendages are linear-lanceolate, as long as the last four segments of the

abdomen, and plumosely haired to the base. The ovisac of thefemale is as

broad as long, three lobed behind with the middle lobe the largest.

Length of a full grown male, including anal stylets, 20 mm., width 6

mm., across eyes 4 mm., clasper 4.5 mm., frontal appendage 5 mm. by 3

mm. The largest females were a little more slender than the males. This

species was first observed at Normal, 111., in clear pools, in April, 1876.

About a fortnight afterward it entirely disappeared. Another species has

been sent me by Prof. Bundy, by whom it was taken in Wisconsin.

Canthocamptus tllinoisens'is, Forbes. Length 1 mm., color light red.

Head and first segment united ; five abdominal segments in male, four in

female. The suture between the first and second segments is not wholly

obliterated above in the female.

Last abdominal segment is deeply and acutely emarginate. Branches

of/urea as wide as long, inner bristle plumose, a little longer than abdomen

;

outer plumose only on outer side, about half the length of the inner. The
second to fifth abdominal segments have each a row of spinules along ventral

portion of posterior margin.

Male with anterior antennae composed of seven joints, the fourth joint

very short. The front outer angle of the third is produced, the blnnt pro-

cess bearing three long bristles surrounding a slender olfactory club which
is as long as the three following joints. The penultimate joint bears a strong

spine or slender appressed process at the middle of its posterior margin.

The five outer joints constitute the grasping organ. The posterior antennae

bear five long bristles at tip, three of which are made prehensile by the oc-

currence of from eight to twelve short articulations in the middle of the hair,

allowing it to be bent forward. At the base of these articulations on the

outer bristle, are two short spinules. Two nearly longitudinal rows of five or

six strong, short spines each appear on the under surface of the outer joint

of the antennule. The secondary flagellum, borne as usual on the middle

of the basal joint, is not articulated, and bears four long bristles, two
terminal and two on distal half of inner side. The outline of the mandible
is exactly like that figured by Glaus, but it bears about ten teeth, the upper

thick and blunt, the inner sharp, slender and longer. Several are notched

*Wanting in vernalis



(15)

at tip. The lower angle bears a long simple bristle. Mandibular palpus
two-jointed, second joint with three long terminal hairs and a shorter spine

attached at basal third of anterior margin, jointed at base and directed
towards tip of joint, like a dactyl. The maxilla and maxillary palpus are
scarcely to be distinguished from those of C. stapliylinus.

The first maxillipeds are three lobed, the outer lobe constituting a long,

strong claw. The second and third are about one-third as long as the first,

and bear each one strong simple spine and one weak branched hair. The
inner lobe is widest, about two-thirds as wide as long. The dactyl of the

posterior maxilliped is spinous on its inner edge, and the same edge of the

hand is ciliate and bears a short, stout, sparingly plumose bristle at its base,

just beyond the tip of the closed dactyl. The width of this joint (the second)
is nearly half its length.

Basal joint of inner ramus of first pair of legs nearly or quite as long as

outer ramus, the second wider but only half as long as the third, and obliquely
truncate. Inner ramus of third pair of legs in male is three-jointed, the

outer two-jointed, chelate. The finger is ovate, truncate, terminating in

two long plumose hairs. The dactyl is linear, curved at base, and twice as

long as finger. The inner ramus of the faurth pair of legs is about half as

long as outer, two-jointed, basal joint short, terminal joint about as long as

middle joint of outer ramus. The Ji/th pair 0/ If-gs is best developed in the

female. In the male the length is not over one-third the width. The basal

portion bears three plumose hairs on its very broadly rounded anterior mar-
gin, of which the innermost is longest. The outer plate is nearly orbicular

and bears five spines on its terminal margin, of which the second from the

internal angle is the longest. Genital plates found in male at posterior

border of first abdominal segment, beneath, are short, slightly expanded in-

ternally, with internal angles rounded, and externally bear three sub-equal
bristles, jointed at base, the inner largest and strongest and semi-plumose.
The antennae of the female are eight-jointed, extending backward to the

first free segment. The basal joint of the Ji/th pair of legs is sub-elliptical

in outline, with the basal half produced externally into a broad, triangular

process which bears the second joint on its posterior margin. The free end
of the basal joint bears six large plumose bristles of which the inner is

longest. The greatest width of the joint is nearly equal to its greatest

length. The second or outer joint is ovate, sub-truncate, spined on each
margin, and bears four plumose bristles at tip and one at the middle of its

outer margin. Its length is about twice its breadth. Same habitat as the

following :

Diaptomus sanguineus, Forbes. This species difiers in some slight re-

spects from the genus to which I have assigned it, as characterized by Claus,

(Die Frei Lebeiiden C<>pepodeii) but not sufficiently to constitute it a new
genus. In the male the fifteenth to eighteenth joints of the right antenna
are thickened, the teeth of the mandible are not at all emarginate, the first

joint of the terminal portion of the lower maxilliped is smaller than the

others, and the right foot of the fifth pair in the male wants the inner

ramus, which is perhaps represented by an immovable blunt spine at the



(16)

inner inferior angle of the second joint. The body of this species is broader

than in D. caUor, the color is throughout a deep red. The antennae are

nearly as long as the body, the eighteenth joint in the female reaching to the

base of the abdomen. The second tooth of the mandible is larger than any of

the remaining six of the series, and is separated from the third by an interval

equal to the width of the tooth. A short feathered bristle appears at the

lower end of the row of teeth. The secondary appendage of the mandibular

palpus is four-jointed, and bears six bristles at its tip and inner margin.

The maxilla has the normal structure, the basal plate, the two cylindrical

processes and the outer ramus (flabellum) and the inner ramus being all

present and symmetrically developed. The first maxilliped is nearly as

broad as long, and bears 15 long hairs on its margin. The basal segment of

the second maxilliped presents four rounded processes on its inner margin,

of which the first is smallest and bears one bristle, the second and third are sub-

equal and bear respectively two and three bristles, and the fourth is largest,

is much produced inferioriy (the rounded lower end being finely ciliate) and

bears four bristles.

The fifth pair of legs in the female is bi-ramose, the inner branch

straight, slender, not jointed, terminating in two short claws; the outer

strong, two-jointed, terminating in a single slightly serrate claw. The sec-

ond joint of this branch bears two slender bristles near the middle of the

outer margin, otherwise the leg is destitute of hairs and spines. The legs of
the fifth pair in the male are very dissimilar. The right leg consists of five

joints ; the basal quadrate ; the second about twice as wide as long, en-

larging distally and bearing a strong blunt spine at the inner, and a longer

one at the outer, inferior angle. The third joint is sub-quadrate, the fourth

clavate, bearing a long bristle at the middle of its outer mai'gin ; and the

fifth constitutes a slender incurved dactyl as long as the preceding joint,

slightly serrate on the distal half of its inner margin, and so jointed as to

close back against the inner margin of the fourth joint, which thus acts as

a hand. The left leg reaches about to the tip of the third joint of the right,

its pedicel contains two large quadrate joints ; the outer ramus two small

joints, of which the terminal one is forcipate at the tip, the inner ramus a

single slender joint on which no armature was seen. The /«rca bears at

tip of each branch four long feathered hairs, and a fifth smaller simple one

at the posterior internal angle. A sixth large and plumose hair is borne at

the posterior third of the outer margin.

Found rather abundantly in a pool fed by a slow spring, ia March and
April, at Normal, Illinois. In several characters, especially those of the

mouth appendages, this species seems closely allied to Ichthyophorba, bear-

ing to some species of that genus a much closer resemblance than to D.
castor, if the figures in Baird's British Entomostraca are at all to be relied on.