274 ORTMANN — DISTRIBUTION OF DECAPODS [April 3 , 



tribution largely on the conditions prevailing in the littoral waters, 

 and generally they follow the physical regions which we have pro- 

 posed for the marine littoral district of the present time. To this 

 there are only a few exceptions, due to special means of dispersal 

 (crossing over continental divides, for instance). For the investi- 

 gation of ancient Geography this genus has no value. 1 



In the following we shall treat of the remaining four families : 

 Potamobiidce, Parastacida, sEgleidce and Potamonida. 



PART I. CHOROLOGICAL MATERIAL. 



A. Chorology of the Families Potamobiid^e and Para- 

 stacidje. (See Fig. i.) 



BIBLIOGRAPHY. 



(a) General Discussions and Systematic Revisions. 



Huxley, Th. : The Crayfish, London, 1879. 



Faxon, W. : "A Revision of the Astacidae " (Mem. Mus. Harvard, Vol. 10, 

 1885). 



1 Coutiere, H. (" Sur quelques Macrures des eaux douces de Madagascar," in 

 C. R. Acad. Sci. Paris, Vol. cxxx, 1900, pp. 1266-1268), discussing the Palae- 

 mons of Madagascar, has advanced some views as to their distribution and con- 

 cludes by putting the (unanswered) question whether this distribution has 

 formed under conditions similar to the present ones or not. This question, how- 

 ever, has been answered in detail by the present writer in the paper quoted above 

 (1891), with which Coutiere seems to have been unacquainted. This is also evi- 

 denced by the fact that some of the peculiarities of distribution in this genus, 

 emphasized by the present writer, are not mentioned by Coutiere — for instance, 

 the relation of the West African species to those of America. Coutiere holds that 

 the West African (not South African) Palcemon vollenhoveni Herkl. is most 

 closely allied to P. bre-uicarpus Haan from Japan, while I regard the relationship 

 to the American P. ja?naicensis (Hbst.) as more important. 



As regards Bithynis hildebrandti Higdf. (1893) from Madagascar, I believe 

 it is hardly possible to connect this species genetically with the type species of 

 this genus from Chile. I think this is a case of convergency. The opinion of 

 Coutiere, that the theory of a Posttriassic connection of Madagascar with India 

 and Africa is to be abandoned, has no support whatever. The distribution of 

 Palcemon, which, according to Coutiere himself, does not go back beyond 

 Miocene times, is absolutely irrelevant to this question, and even the Miocene 

 age of Palamon seems to be doubtful. The presence of identical species on the 

 eastern and western sides of the Cordilleras in South America is no evidence for 

 this, since this distribution is not discontinuous, and the respective species have 

 apparently crossed this chain of mountains, and are actually found in the moun- 

 tains high up in the headwaters of the Anazonas river, for instance. 



