The Crawfishes of Western Pennsylvania. 401 



lateral spine on each margin, by the presence of a lateral spine on the 

 carapace, and by the wide areola. All these characters, however, are 

 common to the next species (C. obscunis~). It differs from the latter 

 in the shape of the copulating organ of the male of the first form, which 

 has no prominent angle on the anterior margin below the base of the 

 terminal teeth, and in the shape of the annulus ventralis of the female, 

 which is flat and has no prominent tubercles. Besides, I have been 

 able to discover, in living specimens, a difference in color. While 

 generally the color of both species is very similar (greenish-olive, with 

 some brown on the abdomen, and a reddish spot on the anterior 

 margin of the carapace below the eye),^ there is a difference in the 

 color of the finger-tips ; in C. propiiiginis the tips are brownish, pre- 

 ceded by a pale or yellowish band, while in C. obscinus there is, prox- 

 imally of the brown tips, a dark green or even blackish band, often 

 followed again by a pale yellowish band. 



There are a few other differences. In C. propinqitiis the rostrum 

 possesses a median keel, which is wanting in C. obsctinis, but in Penn- 

 sylvania specimens of C. propiiiquits this keel is sometimes very indis- 

 tinct. The chelK in C. propinqiius are generally more swollen and 

 less broad and flattened than in C. obscurus, and, except for puncta- 

 tions, are smooth with a double row of small tubercles on the interior 

 margin of the hand. The fingers are straight, in old males they are 

 very slightly gaping at the base, and the outer margin of the dactvlop- 

 odite is only very slightly curved. 



In C. obscitnis the chelse of old males are more flattened and 

 broader, the fingers are widely gaping at the base, and the dactylopo- 

 dite is strongly curved, the curve being S-shaped, Avith a distinctly 

 and strongly concave outer margin. The palm possesses tubercles on 

 the upper side besides the double row on the inner margin ; generally 

 there is a row of tubercles running parallel with the margin toward the 

 middle of the base of the dactilopodite ; sometimes there are additional 

 scattered tubercles between this latter row and the inner margin. 



As has been said, young specimens are not easily identified, since 

 these characters, chiefly the sculpture of the chelae, are not well de- 

 veloped, but I am able to distinguish young males of the second form 

 by the shape of the copulatory organs. Here in both species the 

 prominent angle at the base of the terminal part is missing, but in C. 



1 This spot has been first observed by Williamson in C. obscurus, but by a misprint 

 (p. 13) he states that this blotch is on \\\e posterior margin of the carapace. 



