294 ORTMANN— DISTRIBUTION OF DECAPODS [Aprils, 



Engceus ; in New Zealand, Paranephrops ; in South America, 

 Parastacus ; in Madagascar, Astacoides. All these forms are more 

 or less closely related to each other, only Astacoides from Mada- 

 gascar is rather isolated morphologically, since its branchial formula 

 shows peculiar reductions (only one pleurobranchia on the fifth seg- 

 ment of the thorax, while in all the rest four pleurobranchise are 

 present). In this respect Astacoides resembles the Potamobiidce of 

 the northern hemisphere. 



If it should prove to be correct that the genus Astaconephrops of 

 Nobili, from Southern New Guinea, as its author believes, is most 

 closely related to the New Zealandian Paranephrops, this, together 

 with the occurrence of Paranephrops in the Fiji Islands reported by 

 Huxley, would indicate a distinct direction of the communication 

 between New Zealand and the rest of the world. This would have 

 been over the Fiji Islands in the direction toward New Guinea. As 

 to the connection of the South American Parastaci with the rest of 

 the family, we have hardly any systematic or chorological facts 

 which permit more detailed conclusions. We can only venture to 

 express the opinion that some kind of a connection between South 

 America on the one side and Australia or New Zealand on the 

 other must have once existed. 



In order to get an adequate idea as to the geographical relations 

 of the genus Astacoides we have to recall to our mind a few facts 

 concerning the morphological relations of the Parastacidoz and the 

 Potamobiidcz (see Ortmann, 1901, p. 1289). According to Faxon 

 (1885, p. 126 f.), among the crayfishes of the northern hemisphere 

 it is only the subgenus Cambaroides which approaches those of the 

 southern. Not only the characters mentioned above, the absence 

 of a suture on the telson and the absence of the first pleopods in the 

 female, are common with the southern forms, but there is also a 

 peculiarity in the arrangement of Leydig's olfactory organs on the 

 external flagellum of the antennules which is found in Cambaroides 

 as well as in the Parastacida;. Moreover, if we consider the fact 

 that among the Parastacida it is just the genus Astacoides from 

 Madagascar which shows, in the branchial formula, a similarity to 

 the Potamobiidte (although in other respects the gills are peculiarly 

 developed), it is easy to imagine, in trying to construct a connec- 

 tion between both families — and such a connection must have once 

 existed — that this was located between the area of Cambaroides 

 (Northeast Asia) and that of Astacoides (Madagascar). This would 



