OP ARTS AND SCIENCES. 113 



in the base of the thumb. Carpus triangular, obliquely truncate, in- 

 ner margin armed with a stout spine and some low, scattered tubercles, 

 lower side with two or three teeth and numerous small tubercles. 

 Superior margin of meros with short spines, which are sometimes ob- 

 solescent except the distal ones ; below, the biserial spines are well de- 

 veloped. Sternum hairy. Third pair of legs hooked. First pair of 

 abdominal appendages strong, straight, internal part with a very small, 

 straight apical spine, which does not reach the end of the external 

 part ; external part with two horny terminal teeth, one of which is 

 flat and disc-shaped, the other slender and somewhat curved. 



Length, 97 mm. Breadth, 27 mm. Length of carapace, 51 mm. 

 Length of areola, 18 mm. Width of areola, 1.3 mm. Length of 

 rostrum, 11.5 mm. Length of chela, 50.5 mm. 



Male, form IL Chelipeds smaller, hooks on the third pair of legs 

 smaller, first abdominal appendages without horny teeth at apex. 



Female. CheliB smaller and shortei'-fingered than in the male; 

 annulus ventralis bituberculate in front, each tubercle denticulate. 



Known localities. Texas : Dallas ; east of Canadian River (Coll. 

 U. S. Nat. Mus.). Kansas : Fort Hays. 



This species is remarkable in having the general form of body and 

 claw of the C. Blandingii group of species, while the fact that only the 

 third pair of legs are hooked places it in the C. advena group. The male 

 appendages and the female annulus are very near to those of C. gracilis. 

 In the shape of the body, areola, antennal scale, and claw, it#resembles 

 C. Blandingii, var. acuta, but the rostrum is deeply excavated, and 

 toothless even in small specimens. The full cephalo-thorax and large 

 abdomen seem to indicate that it is not a pre-eminently burrowing 

 species, like its allies, C. gracilis, C. advena, &c. 



There are specimens in the United States National Museum col- 

 lected by the United States Exploring Expedition West of the Hun- 

 dredth Meridian in pools east of the Canadian River. This locality, I 

 presume, is within the limits of the State of Texas. 



§ 3. Third pair of legs of male hooked. First pair of ahdominal ap- 

 pendages of male thick, terminating in two short, recurved teeth. 



a. Rostrum devoid of lateral teeth. 



5. C. ACUMINATUS, sp. nov. 



Rostrum long, tapering, ending in a long, sharp acumen, without 

 lateral spines; upper surface smooth, somewhat hollowed out, margins 

 punctate, ciliate, raised into low sharp crests. Post-orbitul ridges with 



VOL. XX. (n. S. XII.) 8 



