446 AMERICAN TESTUDINATA. Pakt II. 



SECTION IX. 



GENERA OF TESTUDININA. 



Were it not for the circumstance that Linnteus has united all Testudinata into 

 one genus, I believe the classification of this order would long ago have been 

 more natural than it is now. To this day only eight genera have been referred 

 to the family of Testudinina, though its species are very diversified, and exhibit, 

 no doubt, characters indicating generic differences beyond those acknowledged at 

 present, if I may judge from the few that have come under my inspection. The 

 name of Testudo must of course be preserved for that genus to which the 

 common European T. gi'a^ca belongs. Wagler has already separated from it the 

 T. marginata under the name of Chersus, and Fitzinger has applied the name of 

 Chelouoidis to Testudo tabulata, that of Geochelone to T. stellata, that of Psammo- 

 bates to T. geometrica, and that of Megalochelys to T. indica ; while Gray has re- 

 tained the name Chersina for T. angulata, and Dum^ril and Bibron have established 

 the genus Homopus, not to allude to the genera Pyxis and Cinixys of Bell. 

 Although I believe most of these genera to be well founded, I cannot refer to 

 either of them the two species which I have observed in North America. 



Xerobates, Ag. Differs from all other Testudinina in having the front legs 

 compressed, without a sign of a plantigrade palm, and large, flat nails ; the hind 

 feet are plantigrade, with a round surfiice. There are only a few large scales 

 side ]jy side upon the forehead. The head is very broad across the temporal 

 muscles ; the region of the eyes, nose, and mouth is short ; and the top of the 

 skull nearly horizontal between the eyes. The mouth spreads out widely immedi- 

 ately behind the symphysis. The lower jaw is high, and spreads apart from alcove 

 downward. The inner edge of the horizontal alveolar surface of the upper jaw 

 descends to a sharp ridge all around ; from it another ridge reaches across the 

 surface at the symphysis to the vertical surface. The ridge which fits into the 

 furrow of the lower jaw is very prominent and sharp ; it is interrupted at the 

 front end only for a short distance. The inner edge of the alveolar surface of 

 the lower jaw rises no higher at its front than at its hind end, but is nearly 

 horizontal, and nowhere as high as the outer alveolar edge ; the ridge thus formed 

 is interrupted for only a very short distance at the front end. In the horny 

 sheath of the alveolar edge and the inner ridge at the symphysis there is a 

 notch, which fits over the opposite ridge of the upper jaw. The oblong, rounded 

 plastron is curved upward at the ends. 



