288 OKTMANN — DISTRIBUTION OF DECAPODS [Aprils, 



assume the same or a similar form. If, finally, Faxon says that the 

 shape of the chelae in Cambaroides resembles those # of Cambarus, he 

 means apparently only the general weak development of them, and 

 we must bear in mind that many Cambari are more like typical 

 Potamobii in this respect. 1 



Thus the view seems supported that Cambaroides is not so very 

 closely related to Cambarus, as has been hitherto supposed, and 

 that the similarities which were emphasized are due only to con- 

 vergency. If we peruse the comparison of the characters of Camba- 

 roides, Pota?nobius and Ca?nbarus given by Faxon (1885, pp. 126, 

 127), we find that Cambaroides is in some of them more isolated, 

 and that it resembles in others even more the West American 

 species of Potamobius. (For instance, the lack of a transverse 

 suture of the telson ; the shape of the second male abdominal ap- 

 pendage ; the lack of the first abdominal appendage in the female.) 



The conclusion drawn from the foregoing is that in certain 

 respects (telson, second pleopods of male, first pleopods of female) 

 Cambaroides represents a type that points to the West American 

 Pota?nobii, while the European species are more divergent from it, 

 and there is nothing that opposes the view that this subgenus 

 (which might as well be regarded as a separate genus) forms the 

 starting point on the one side for the European Potamobii and on 

 the other for the American Potamobii, while subsequently it has 

 changed itself and become different from both (in the male copula- 

 tory organs). 



The subgenus Cambaroides is restricted to the northeastern parts 

 of Asia (region of Amur river, Korea, North Japan). The exact 

 boundaries of its range have nowhere been located positively, and 

 it is not impossible that in the Siberian and northern Chinese 

 mountains other representatives of it may exist. For the present 

 the area from which species of Cambaroides are known is absolutely 

 separated from the European area of Potamobius. 



As regards the latter, its centre is apparently in Southern and 

 Central Russia. From these parts the different species extend into 

 Western Europe, southward to Central Spain, Middle Italy and 

 Greece, and in Russia one species passes southward across the 

 Caucasus Mountains, Eastward a species is found as far as Turke- 



1 Some other characters of Cambaroides indicate that this subgenus differs 

 from Potamobius as well as from Cambarus, and these are characters which 

 approach it to the crayfishes of the southern hemisphere. Compare below. 



