ASTACUS LEPTODACTYLUS. 303 



crayfishes. Gerstfeldt, wlio has had the opportunity of 

 examining large series of specimens, concludes that the 

 Pontocaspian crayfishes and A. nohilis are all varieties 

 of one species. Kessler, on the contrary, while he 

 admits that A. angulosics is, and A. pachjpus may be, 

 a variety of A. leptodactylus, afiirms that the latter is 

 specificallj' distinct from A. nohilis. 



Undoubtedly, well marked examples of ^4. leptodactylus 

 are very different from A. nohilis. 



1. The edges of the rostrum are produced into five or 

 six sharp spines, instead of being smooth or shghtly 

 serrated as in A. nohilis. 



2. The fore part of the rostrum has no serrated 

 spinous median keel, such as commonly, though not uni- 

 versally, exists in A. nohilis. 



3. The posterior end of the post-orbital ridge is still 

 more distinct and spiniform than in A. nohilis. 



4. The abdominal pleura of A. leptodactylus are nar- 

 rower, more equal sided, and triangular in shape. 



5. The chelfe of the forcejDS, esjiecially in the males, 

 are more elongated : and the moveable and fixed claws 

 are slenderer and have their opposed edges straighter 

 and less tuberculated. 



But, in all these respects, individual specimens of 

 A. nohilis vary in the direction of A. leptodactylus and 

 vice versa; and if A. angulosus and A. p)a^<^hypus are 

 varieties of A. leptodactylus, I cannot see why Gerst- 

 feldt's conclusion that A. nohilis is another variety of 



