GEOGRAPHICAL DISTRIBUTION 



95 



there are not a few resemblances between this Eastern Asiatic 

 and the American fauna. The Urodela thus lend no support to the 

 usual division of the Periarctic into a Palaearctic and a Nearctic 

 sub-region. Nor is it possible to divide the Palaearctic into a 

 Eurasian and a Mediterranean province. We have in this case 

 to distinguish between an American, an Asiatic, and a European 



S.MECODONTA. .^ ICHTHYODEA. 



FIG. 16. Map showing the distribution of the Urodela. " Ichthyodea " = Amphiuruidae 

 + Proteidae + Sireiiidae. 



fauna. The Asiatic or Eastern Palaearctic sub-region assumes the 

 central position, at least from a merely geographical point of view. 

 It would be unjustifiable to assume a spreading from this centre 

 into Europe, and, on the other hand, into America. The centre 

 existed more probably in the Arctic circle, now devoid of Urodela. 



So far as mere numbers of species are concerned the huge 

 Asiatic or Eastern Palaearctic region is the poorest, but it is 

 also the least explored, and China will probably yield a good 

 many new forms. We know at present only 15 species, nearly 

 all from the eastern half. These 15 species represent no less 

 than 11 genera, 8 of which (=73 per cent) are peculiar to the 

 sub-region. Next comes the Western Palaearctic or European 

 sub-region with about 21 recent species of 5 genera, 4 of which 

 are peculiar. America is by far the richest, with no less than 

 66 species (36 eastern, about 16 western, and the rest Central 

 American, etc.), belonging to 19 genera, 17 of which ( = 90 per- 

 cent) are peculiar to the New World. But this richness in species 

 is due mainly to the abundance of the two genera Amblystoma and 

 Spelerpes, just as Europe is characterised by its many Tritons. 



One of the most striking features of the Asiatic sub-region is 



