LIST OF CRUSTACEANS.


epistoma transverse, truncate, or in some individuals emarginate, sides oblique;
maxillipedes coarsely barbate on inner aspect, sparingly so below; chele
much
as in C. virilis, but somewhat more slender, fingers punctate and costate
above
with rounded tubercles on contiguous edges, outer one hairy at base; movable
finger with two rows of serrate teeth on inner margin, inner margin of chele
with two rows of teeth; carpus with one sharp spine on middle of lower anterior
margin and a larger one at middle of interior margin; brachium with two rows
of sharp teeth below; third joint of third thoracic legs hooked; first abdominal
legs of male long, bifid, external part longer, both recurved, inner often
some-
what enlarged near tip. These legs reach to base of first thoracic pair when
the
abdomen is flexed. Length of areola contained one and one-third times in
line
from cervical suture to tip of acumen. Racine, Ironton, Wis. Normal, Ill.
Not common.
C. debilis. Bundy. Bulletin No. 1, Ill. Mus. Nat. Hist., 1876.
Rostrum wide, quadrangular, slightly concave above, teeth prominent, mar-
gins nearly parallel, acumen short and flat; cephalothorax slightly depressed,
punctate above, granulate on sides; lateral teeth acute; areola narrow, widest
behind; antennal plates slightly longer than rostrum; antennae slender, reaching
to base of telson; epistoma transverse; third maxillipedes bearded on inner
and
lower aspects; chele with two rows of teeth on interior margin; fingers tuber-
culate on contiguous margins, outer one hairy at base, both costate and punctate
above; third joint of third thoracic legs of male hooked; first abdominal
legs of
male long, bifid, nearly straight, outer ramus longer, recurved; inner ramus
more abruptly recurved near apex, not enlarged near apex as in the preceding
species; tubercles on basal angle inconspicuous.
Ironton, in company with C. propinquus. A single individual found at Sauk
City.
C. gracilis. Bundy. Bulletin No. 1, ILl. Mus. Nat. Hist., 1876.
Rostrum short, wide, depressed, toothless, concave above, nearly right-angled
in front; cephalothorax laterally compressed, smooth above, granulated on
sides;
areola none, cephalic carinae prominent, ending posteriorly in callosities;
antennal
laminva small and narrow; eyes small; antennae slender and short; epistoma
rounded in front; third maxillipedes hairy on interior and posterior margins;
chelm large, smooth below, punctate above, strongly toothed on inner margins;
fingers slender, gaping at base, depressed, contiguous margins irregularly
tuber-
culate, outer one incurved, wide at base, movable one longer; carpus with
one
large and several small teeth on inner margin; brachium with two rows of
sharp
teeth on inferior margin; third joint of third thoraic legs of male hooked;
first
abdominal legs of male truncate, with several small apical teeth, of which
the
inner one is longest, slender, and directed obliquely outward; bases of these
legs
narrow and inserted in deep sinuses in the first abdominal segment; interpedal
space long, narrow, reaching half way from basal tubercles to apex of legs.
Ventral annulus of female movable, small and round. It consists of two half
rings, each of which embraces one end of the other. Two tubercles on the
anterior border are separated by a slight furrow that widens behind, covering
the posterior portion. The posterior border is notched.
Low prairies in the neighborhood of Racine (Dr. P. R. Hoy). Normal, Ill.
(Prof. Forbes).
C. obesus. Hagen. One of our most abundant species, frequenting ponds
and meadow ditches. It is pre-eminently our burrowing species. The preceding
species, according to Dr. Hoy, has the same habit.
C. Bartonii. Erickson. Lake Superior (Hagen).


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