i«7o.] 607. ^^Qj^p^ 



postabdominal regions of throe individuals. The only reason for such 

 reference of Llie latter, is their superficial texture, in which they resemble 

 tlie cheles, and differ from the corresponding parts in the two other species. 

 The cheles are short and thick, the section of the stoutest proximal 

 part being an oblique oval. The inferior edge is thinned by longitudinal 

 contraction above and below it. The fixed process is of a rather short 

 conic form. The surface is granular tuberculate, except on the convex 

 faces, whei-e it is finely vermiculate rugose. 



M. 



Length last segment cheles, , . . . . 0.039 



Width 021 



Proximal transverse diameter 013 



The cephalothorax associated is quite similar to that of A. subgrundi- 

 alis, and may possibly belong to it. It however, differs in the finely ver- 

 miculate rugose character of its surface. The rug^ are generally trans- 

 verse on the back and sides. The supra-anteunal lamina is exhibited in 

 a clear manner ; it is as long as the spine of the muzzle, and as wide at 

 the base. 



The superior surfaces of the abdominal segments are marked with a 

 delicate vermiculate rugosity, like that of the last specimens. In A. sub- 

 gruncUalis, it is impressed punctate. This species also differs from the latter 

 in that the transverse marginal lamina of the first postabdominal segment, 

 is narrower than in the latter, its width not equaling twice that of one of 

 the others, instead of being four times as wide. The succeeding lami- 

 nag are acuminate elongate, and slightly curved forward. It is, however, 

 quite uncertain as to whether these postabdominal specimens belong to 

 the species which has the stout cheles. Some of the specimens indi- 

 cate individuals larger tlian those referred to A. subgrundialis. 



From the same locality and collection as the last. No. 9779. 



General kemaeks. 



The preceding species differ from those at present inhabiting North 

 America, as I have been able to determine by examining the excellent 

 monograph of the latter, published in the catalogue of the Museum. 

 Compar. Zoology, by Dr. J. H. Hagen. Theydifferfromallof theminthe 

 prominence and acumination of the lateral margins of the jjostabdominal 

 segments. In the serrate simple frontal process, the first described re- 

 sembles the Aslacus gambelU Girard, but its process is longer and nar- 

 rower. 



I have already described * twelve species of fishes from the same local- 

 ity and deposit, whence these Astaci were procured. 



* Proceed. Amer. Philos. Soc. 1870, December 8. 



