302 AMERICAN TESTUDINATA. Part II. 



In the sub-order of Amyclfe, the same features which characterize the Chelonii 

 obtain again, though within still more restricted limits. The aquatic Amyda3 have 

 a wider range than the terrestrial ; and while the lower representatives of the 

 sub-order are fluviatile, the higher ai'e terrestrial. The lowest Amydaj, the Triony- 

 chidiP, have truly the widest distribution ; for while in the Old World they are 

 chiefly limited to the tropical fresh w^aters, in the New World they are only 

 found within the temperate zone of North America, extending as far north and 

 as high in the mountains as any other Turtles, indeed much farther north, and 

 higher up, than any land Turtles, and even beyond the natural boundaries of the 

 EmydoidtB. The family of Chelydroidte is already much more restricted in its range, 

 being limited to the temperate zone of the eastern side of the North American 

 and of the Asiatic continents. The Chelyoida?, on the contrary, are circumscribed 

 within the fresh waters of tropical South America ; whilst the Cinosternoidse extend 

 over the temperate parts of North America, over Central America, and over the 

 warmer regions of South America. The Hj^draspids, on the contrary, prevail in 

 South America, and extend also to Southern Asia, to Africa, and to New Holland. 

 The family of Emydoidw, which is, as it were, the central type of the Amyda3, 

 is the. only one among the fresh-water Turtles which has representatives simulta- 

 neously in North and South America, in Europe, in Africa, and in Asia, though 

 the range of the individual species is very limited in this family also, much more 

 so, indeed, than the species of the lower families of the aquatic Amydte, or 

 those of the Chelonii. The highest Amydaj, the Testudinina, or land Tiu'tles, are 

 the most limited in their range, if we contrast them with the whole number of 

 fresh-water Testudinata, for they do not extend beyond the limits of the warmer 

 jiarts of the temperate zone, while the aquatic Amydaj are not only found in 

 the tropical fresh waters, but also in those of the Avarm, and even of the colder 

 parts of the temperate zone. It may perhaps seem unnatural, that I should 

 thus contrast the Testudinina, ^vhich constitute only one family, with the many 

 families of fresh-water Amydte ; but it is just the object of physical geography 

 to ascertain what are the natural relations between the physical conditions of the 

 surface of the globe and the organized beings which live upon it. 



I shall enter into more details respecting the special distribution of the North 

 American Testudinata, after I have considered more fully their generic and specific 

 relations to one another. There is one more point, however, Avhich deserves to be 

 noticed in this connection. The Chelonii proper, which are the lowest, and at the 

 same time the only marine Testudinata, are also the largest repi'esentatives of the 

 whole order ; next in size are some of the fresh-water Amydte, of the family of Che- 

 lydroidoe, which are veiy large, as are also some of the Testudinina. The average 

 size of the fresh-water Amydse exceeds, nevertheless, that of the terrestrial ones. 



