38 DISTRIBUTION OF TORTOISES. [CH. I 



birds are dealt with later in giving the characters of the 

 different regions and sub-regions. 



Distribution of Chelonia. 



When Mr Wallace wrote his text-book upon Geo- 

 graphical Distribution he was able to make but few 

 remarks upon the distribution of the Chelonia, since the 

 classification was in a very imperfect state, and therefore 

 the bearing of the facts of distribution were not apparent. 

 Now however, thanks to Mr Boulenger's catalogue of the 

 order, we are in a position to deal with the distribution of 

 the group in a manner more satisfactory than was open to 

 Mr Wallace. 



Mr Boulenger divides the Chelonia primarily into two 

 great groups, the Athecae and the Thecophora. The first 

 group is distinguished by the fact that the vertebrae 

 and ribs are free and not connected with the bony 

 exoskeleton. As it only contains a single family, genus, 

 and species, Sphargis coriacea of entirely marine habitat, 

 it need not concern us any further here. The second 

 division of the Chelonia is made up of three super-families, 

 the Cryptodira, the Pleurodira and the Trionychoidea. 

 These together contain eleven families, of which there are 

 seven in the Cryptodira, three in the Pleurodira and only 

 one family in the Trionychoidea. 



Of the first super-family the families Chelydridse (two 

 genera), Dermatemydidaj (three genera), Cinisternidae 

 (one genus) are confined to the American continent. The 

 Platysternidae (one genus) range over S. China, Siam and 

 Burma; there is but a single species which has this wide 



