24 CHERSITES. 



8. The mouth is small, with the horny or cutting margin of the jaws often 



serrated. 



9. The tongue is thick and papillated, and fills the concavity of the lower jaw. 



10. There are never barbels at the chin, or cutaneous appendages at the neck. 



11. The extremities are of equal length; the hand is confounded with the fore- 

 arm, having only a slight fold at the carpus; the fingers are not in general 

 distinct, but are united in a mass and covered by a thick skin. With one 

 exception, all have five nails, which correspond with the phalanges. The 

 posterior extremities are clavate, and often resemble much the legs and feet 

 of the elephant, and have four nails. 



12. The tail is short and conical. 



13. The eggs are round, and have a hard shell. 



Of Chersites, only two genera inhabit the United States, Testudo and Cistuda; 

 which last genus I have thought best to unite with this flimily, because it is 

 really a land animal and agrees perfectly with that tribe in its habits. In some 

 parts of its organization, however, as in the extremities, the genus Cistuda 

 approaches that of Emys so much, that it may fairly be considered a connecting 

 link between the land and fresh-water forms of Tortoises; yet it stands much 

 better at the termination of the Chersites, than at the head of the Emyda?. 

 Its proper place I consider to be after the genus Pyxis, of Bell; which is the 

 beginning of the transition. In this the anterior portion only of the sternum is 

 movable; and here for the first time is seen in the extremities "an approach to 

 the palmated conformation of the Emydae, and the claAvs are observed to assume 

 somewhat of the length and sharpness that characterize the fresh-water family." 

 In Cistuda, both valves of the sternum are movable, and the extremities still 

 more depressed. 



