CAMBARUS. ail 
Girard’s description of C. rusticus is as follows : — 
“ Rostrum narrower than in both C. afimis and C. Peale’, and, besides, 
concave on the sides. Terminal poimt shorter than either of the preceding 
species [C. pellucidus, affinis, Oreganus, and Peal]; anterior pair of abdom- 
inal legs (in the male) elongated, slender, with their tip curved inwards, 
whilst the same tips are straight in C. affinis, and twisted in C. pellucidus, 
The dorsal area is broader than in C. Pealei. 
“ Locality. — The Ohio, at Cincinnati.” 
This description does not fit very well, but Dr. Hagen examined one 
of Girard’s types and ascertained its identity. 
Closely related to the above described form are Hagen’s C. placidus and 
C. guvenilis. I find so many specimens among the material at my disposal 
which combine characters of these three, that I am led to consider them 
all as varieties or forms of C. rusticus. 
In the type (male, form I.) of C. placidus, from Quincy, Ill. (M. C. Z., No. 
296), the rostrum is longer and narrower than in the typical CL rusticus, 
with longer acumen and lateral spines; the hands have long, straight, non- 
tuberculate fingers, like the C. rusticus from Lake Superior mentioned above ; 
the rami of the first pair of abdominal appendages are a little recurved, and 
want the projecting shoulder at the base of the rami on the anterior border ; 
the antennal scale is subtruncate, with longer apical spine. The types from 
Lebanon, Tenn. (M. C. Z., No. 289), are second-form males and females. They 
differ from the Quincy specimen in having a well-developed internal median 
spine on the carpus, and an acute though small lateral spine on the carapace ; 
in some of these specimens the rostrum is slightly carinated near the tip; the 
external ramus of the first abdominal appendage, instead of being straight, 
as in the typical C. rusticus, is a little recurved at the tip. Of the types from 
Texas (M. C. Z., No. 170) there are now five in the Museum collection, four 
males of the first form, one male of the second form. In three of the first 
forms a projecting shoulder is prominently developed on the anterior border 
of the first pair of abdominal appendages, as in C. rusiicus and C. suvenilis ; 
in the fourth specimen it is also present, but less marked. Two or three of 
these examples further agree with the typical C. rus/icus in the form of the 
chela. The internal median carpal spine is strongly developed, the lateral 
spine of the carapace small and acute, the inner row of inferior spines of 
the meros well pronounced. The first pair of abdominal appendages in all 
the first-form male types of C. placidus are a little longer than in C. rusticus. 
