132 THE NEOG^IC REALM. [CHAP. 



Thyropoda, and in Madagascar, where there is the sole member of 

 the allied genus Myxopoda^ may be an analogous instance. 



In the second family of the pleurodiran Chelonia, the Chelyidcz, 

 which are now restricted to South America and Australia (the 

 genera in the two areas being distinct), there is at present no 

 evidence of the derivation of the Australian forms, but of the 

 Neogaeic types Platcmys is represented in the Cretaceous of the 

 United States, and Hydraspis in the Eocene of Bombay. Although 

 the northern origin of the family is thus proved, the explanation 

 of how the existing forms attained their present distribution is 

 very difficult. Possibly Hydraspis may have reached South 

 America by way of Africa; but it is difficult to believe, in the 

 absence of its remains, that Platemys survived in North America 

 till the late Miocene communication with Neogaea was estab- 

 lished. 



Among snakes, the boas of the genera Corallus and Boa are 

 confined to South America and Madagascar, and thus have 

 precisely the same distribution as Podocnemis. Now although true 

 boas are unknown as fossils, the allied extinct genus Paleryx 

 occurs in the European Oligocene, thus pointing to the northern 

 origin of the group, which has probably reached South America by 

 way of Madagascar and Africa. 



Another remarkable case is afforded by the limbless lizards of 

 the family Amphisbcenidcz, which are now almost equally divided 

 between South America and South Africa, although one genus 

 extends into the Mediterranean area, and two are found in North 

 America ; the two genera Amphisb&na and Anops being common 

 to South America and Africa, while the northern ones are different. 

 The northern origin of the family is, however, indicated by the re- 

 cent discovery of fossil forms 1 in the White River Oligocene of the 

 United States. Here the evidence strongly points to a southern 

 connection between Neogaea and Africa; Tertiary forms having 

 probably existed in Europe or Asia as well as in North America. 

 A second instance that may be cited among lizards is the family 

 of the Iguanidcz, which while now mainly Neogaeic, has represen- 

 tatives in the warmer parts of North America, and also includes 



1 Baur, American Naturalist, Vol. xxvii. p. 998 (1893). 



