284 ANNALS NEW YORK ACADEMY OF SCIEXCES 



Pleurodira. — Now limited to the three southern continents. Ilobirctic in the 

 later Mesozoic and early Tertiary, and the extinct Amphichelydia from which 

 they are descended were likewise a Holarctic jri'oup. The occurrence of closely 

 related genera in South America and Madagascar is used in support of a 

 Brazilian-Ethiopian-Malagasy land connection. It would be interpreted in 

 conformity with the views here advocated, as due to common descent or to 

 parallel evolution from Tertiary Pleurodira of Holarctica. 



Trionychidcr. — The distribution of this grouj* is exceptional in that it is en- 

 tirely absent from the Neotropical region and the Pacific coast of North 

 America, while common to eastern North America, the Ethiopian, Oriental and 

 southeastern I'ala-nrctic regions and New Guinea. Ameghino records Trionux 

 from the Notostylops Beds of Patagonia,"' indicating if the identification be 

 correct that the group was formerly present in South America. It is found 

 abundantly in the Cretaceous and Tertiary of North America and in the older 

 Tertiary of Europe; absent from Australia and Madagascar. 



Presumably this is a relict-distribution of an ancient group, whose facilities 

 for transportation were relatively limited. It should be noted that the hy- 

 pothesis of over-sea transportation on rafts would be less applicable to aquatic 

 animals than to their terrestrial relatives, as they would be less likely to be 

 carried out to sea on floating vegetation, on account of their ability to leave 

 it at will for the shore. But the absence of the group from the Neotropical 

 and Western Nearctic, and its presence in New Guinea, are anomalous features. 



CEOCODILIA 



The crocodiles are usually regarded as the most conservative of the 

 reptilian orders. This is true enough, so far as adaptive specialization 

 from the primitive amphibious environment into the higher plane of ter- 

 restrial habitat is concerned. Their expansional tendencies have been in 

 the other direction, towards invasion of the marine province. 



The present geographic distribution of the group is as follows : 



Narrow f Gavialis, India, 

 snouted 1 Toniiatotna, East Indies. 



Broad 

 snouted 



Allifjator. Southern United States, China. 



Crocodilus, Africa, southwest Asia, Oriental and northern Austra- 

 ^ lian regions, tropical America and West Indies. 



CainKui, Tropical America. 

 Osteolcemus, West Africa. 



This is very clearly a remnant-distribution and is explained, at least in 

 part, by the occurrence of crocodiles in the Tertiary. Fossil Crocodilia 

 are abundant in the early Tertiarics of Europe and North America. The 

 European species, according to Zittd,^""' belong partly to Crocodilus, 



i<" Fl. Ameghino : "Age des Formations Sedimentaires de Patagonie,"' Anal. Soc. 

 Cient. Argent., torn, l, liv. p. 52 of separata. 1003. 



i»« K. A. VON ZiTTEi. : Grundziige der I'aUiontologle, 2e Aufl., ii Abteil., s. 272. 1911. 



