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Show 176 DR. J. E. GRAY ON THE TORTOISES. [Mar. 1 1, logy,' p. 39, t. 3, it appears to agree with the other American species. If it does, this is another reasou why it should not be referred to the genus Lutremys, in which Agassiz has placed it in his ** Contributions.' Tribe I. CISTUDININA or North-American Box-Tortoises. The temporal muscle only covered with skin. The skull without any zygomatic arch between the orbit and the ear-bones. Lobes of the sternum moveable at all ages, unequal ; front shorter, almost free from the symphysis; the hind fixed, narrow, elongate. 1. CISTUDO. CISTUDO CLAUSA. Skeleton in the British Museum. Cistudo clausa, Owen, Cat. Mus. R. C. S. p. 192. n. 998 (skeleton), 1009 (skull of young). Professor Owen describes a peculiarity in the neural arch of the atlas and the other vertebrae, and in the bones of the feet; but he does not notice the absence of the zygomatic arch in the skull. Fig. 3. Cistudo clausa. Skull in College-of-Surgeons Museum, No. 999:-Nose-hole square, moderate ; orbit excessively large; tympanic cavity oblong, erect ; upper jaw with a straight lateral edge and a broad central part; palate flat, internal nasal apertures anterior, with a broad triangular concavity behind them with a central ridge ; alveolar plate smooth, narrow in front, rather wider behind ; alveolar surface of the lower jaw rather wide, concave. |