CI OGRAl'HICAL DISTRIBUTION. 



.55 



the Upper Cretaceous. In England species existed during the Eocene and a species 

 of the same epoch has been described from India as a Hydraspis, a genus now 

 existing in South America. It is worthy of note, too, that in North America the 

 Pleurodires apparently disappeared long before the Amphichelydia did, the stock 

 that gave origin to the Pleurodires. The Amphichelydia continued on into the 

 Bridger and the Uinta. 



It will be observed from the map (fig. 16) that the Trionychids occupy the 

 habitable portion of North America east of the Rocky Mountains; Africa south of 

 the Sahara Desert; Asia south of the Sayanskii and Yablonoi Mountains and 

 between the Persian Gulf and the Caspian Sea; and most of the East Indian islands, 

 including New Guinea. Altho the oldest-known representatives of the Trionychida? 

 have been found in the middle of the Upper Cretaceous of North America and altho 

 that continent is still inhabited by at least 6 species, it is Asia that furnishes the 

 greatest number of living forms of the family, at least 15 species having been 

 described from that region, including the islands appertaining to it. In Africa there 

 occur about 6 species, so far as now known. As in the case of the Cryptodires, the 

 trionychids have prest southward close to Australia, without having succeeded in 



FlG. 16. Map showing the distribution of the Trionychidie. 



reaching it, Pelochelys cantons having been reported from New Guinea. No Triony- 

 chida? have been found in the Tertiary beds of the Fayum, Egypt. Considering 

 the fact that true trionychids antedate known pleurodirids, it appears strange that 

 the former were not able to reach Australia with the pleurodirids; more especially 

 since the trionychids are, and have been since the Judith River epoch, excellent 

 swimmers. A problem fully as hard to solve is the absence of trionychids from the 

 continent of South America. So far as we can judge, they might easily, within 

 rather recent geological times, have made their way thither from North America. 

 Aoain, Ameghino has described what he regards as a species of Trionyx from the 

 Cretaceous of Patagonia. The description is very brief and no figures have been 

 furnisht. If representatives of the superfamilv had reacht the continent by the 

 time of the Upper Cretaceous it is remarkable that they were not able to maintain 

 themselves there. No region appears to be better adapted than this for river-loving 

 species of turtles. 



In Europe we have another illustration of the fact that animals may be driven 

 from a region in which they have once obtained foothold. No species of the 

 superfamilv now occupies that region; but numerous species did exist there during 

 the Eocene, the Oligocene, and the Miocene. It has not yet been determined 

 what the influences were that operated against them. 



