ASTACUS LEPTODACTYLUS. 3038 
crayfishes. Gerstfeldt, who has Had the opportunity of 
examining large series of specimens, concludes that the 
Pontocaspian crayfishes and A. nobilis are all varieties 
of one species. Kessler, on the contrary, while he 
admits that A. angulosus is, and A. pachypus may be, 
a variety of A. leptodactylus, affirms that the latter is 
specifically distinct from A. nobilis. 
Undoubtedly, well marked examples of A. leptodactylus 
are very different from A. nobilis. 
1. The edges of the rostrum are produced into five or 
six sharp spines, instead of being smooth or slightly 
serrated as in A. nobilis. 
2. The fore part of the rostrum has no serrated 
spinous median keel, such as commonly, though not uni- 
versally, exists in A. nobilis. 
8. The posterior end of the post-orbital ridge is still 
more distinct and spiniform than in A. nobilis. 
4. The abdominal pleura of A. leptodactylus are nar- 
rower, more equal sided, and triangular in shape. 
5. The chele of the forceps, especially 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. nobilis vary in the direction of A. leptodactylus and 
vice versd; and if A. angulosus and A. pachypus are 
varieties of A. leptodactylus, I cannot see why Gerst- 
feldt’s conclusion that A. nobilis is another variety of 
