4 o REPTILES 



the western hemisphere is limited by latitude 50 and in the 

 eastern by latitude 56°, the most remarkable feature is the 

 limitation of the pleurodiran group (in which the neck is 

 retracted by a horizontal flexure) to the southern hemisphere, 

 where they occur in all the three continents, and in Australasia 

 to the exclusion of the cryptodiran group (in which the neck is 

 retracted by an S-like flexure in a vertical plane). Of the two 

 chief families of Pleurodira, the Pelomednsidce are common to 

 Africa, Madagascar, and South America, while the Chelyidce 

 occur in South America and Australasia (exclusive of New 

 Zealand), although there is no generic type common to the 

 two areas. As regards the Trionychoidea, or soft river-tor- 

 toises, the group is confined to Africa, Tropical Asia, and 

 Eastern North America, to the exclusion of South America 

 and Australasia ; the distribution in America and Asia being 

 thus comparable to that of alligators, although more extensive 

 in the latter area. Of the terrestrial and fluviatile families of 

 the Cryptodira, the snappers, Chelydridiz, are American, 

 ranging as far south as Ecuador, but are represented in the 

 Miocene of Europe. The Dermatemydidce and Cinosternidce 

 are North and Central American ; the Platysternidce are 

 confined to Eastern Asia, and the Testudinidce, especially as 

 represented by the typical land-tortoises of the genus Testudo, 

 are cosmopolitan, with the exception of being unknown in the 

 Australasian area. 



The Crocodilia are found in the warmer regions of all the 

 great continents, inclusive of Northern Australia, as well as in 

 the larger tropical islands. Crocodiles (Crocodilus) in the New 

 World are confined to Central America and the northern ex- 

 tremity of South America, but elsewhere their distribution is 

 coextensive with that of the order. The distribution of true 

 alligators {Alligator) has been already referred to ; but 

 caimans or South American alligators (Caiman) are natives of 

 Central and South America. On the other hand, the long- 

 snouted gharials (Garialis and Tomistoma) are restricted to 

 India and the Malay countries. 



The Rhynchocephalia are confined at the present day to 

 New Zealand, whose only other reptiles are geckos and skinks. 



Chamaeleons are an essentially African and Malagasy group, 

 with outlying forms in the south of India and Arabia and in 



