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Show 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 animals ; 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 flattened 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. I. 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* |