1873.] ALVEOLAR SURFACES OF TORTOISES. 723 



for separating the species and the various modifications that they 

 assume. 



In the * Catalogue of Shield Reptiles,' as we then had no skulls 

 of certain genera in the collection, I was obliged to describe the 

 alveolar surface of the beaks as they were seen in the preserved ani- 

 mals ; but the beaks do not give the same idea of the surface as 

 the skull itself; and in this paper I have remedied this evil by 

 describing the alveolar surface of the skulls that we have since 

 obtained. 



Fitzinger, in one of his compilations, divided the Tortoises, from 

 their descriptions, into genera, and gave names to them, but did not 

 characterize them in any recognizable way. No doubt the sticklers 

 for priority will consider and quote these genera as Fitzinger' s, thus 

 giving the premium to such proceedings. Professor Agassiz, in his 

 ' Contributions,' characterizes a new genus under the name of 

 Xerobates, and refers to some of Fitzinger' s genera. I have here 

 attempted to arrange the species according to the forms of their 

 skulls and the alveolar processes, which is no doubt consistent with 

 their habits and food. 



Section I. The alveolar surface of the upper and lower jaws flat- 

 tened for nearly the whole of their length ,• two longitudinal 

 ridges on each side ; the outer ridge of the upper jaw fitting 

 into the linear groove of the lower jaw. Lower jaw stout and 

 strong. The dorsal and sternal disk solid, undivided. 



Tribe I. Xerobatina. 



Alveolar process of upper jaw with two parallel ridges, which do not 

 quite reach the centre, which is flat, and has a central longitudinal 

 ridge from the front to the hinder ridge. Lower jaw with a ridge 

 on each side in front of the linear alveolar concavity, continued to 

 near the centre, which has a transverse groove across it from the 

 front to the back edge. 



1. Xerobates. 

 Xerobates, Agassiz, Contrib. i. 446. 



Xerobates gopher. (Plate LX. fig. 1, alveolar processes of 

 jaws.) 



X. carolinus, Ag. Cont. i. p. 447. 



See also X. berlandieri, Ag. 1. c. p. 447. The specimen in the 

 Museum only appears to be a variety of the former species. 



Tribe II. Megalochelyina. 



The lower jaw with a ridge on each side of the linear alveolar 

 concavity, continued to near the acute central prominence in the 

 front of the jaw, which has a transverse ridge to the hinder edge of 

 the jaw. Alveolar process of the upper jaw with two parallel ridges, 

 with a deep circular concavity in front. 



46* 



