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Show 398 DR. J. K. GRAY ON THE GENERA OF TURTLES. [Apr. 1, triangular, truncated in front, and slightly notched behind in the centre. The hinder pair of caudal plates are very long, much longer than broad, four-sided, the hinder and outer sides shortest; and the hindermost lateral plate has a straight inner edge, aud is not angular and produced as in Eremonia elongata. The dorsal shield of this genus has some resemblance to the shield of Eremonia elongata in the large size of the caudal marginal plates ; but of the latter genus the head and limbs are unknown : it belongs probably to the family Caouanidee, as it has five costal shields on each side; while this has only four, and belongs to Cheloniadae. The shields of the two genera may be thus distinguished :- Onychochelys. Costal plates 4.4. First vertebral shield triangular, with lateral angles truncated, much longer than broad. Second, third, and fourth vertebral shields hexagonal; lateral angles produced, as broad as long. The penultimate marginalshield with a straight inner edge. Eremonia. Costal plates 5.5. First vertebral shield hexagonal, as broad as long. Second, third, and fourth vertebral shields very long, oblong, four-sided, with the middle of the sides rather prominent, much longer than broad. The penultimate marginal shield prominent, angular in the middle, projecting between the last costal and the last vertebral shields. 1. O N Y C H O C H E L Y S KRAUSSI, Gray, Hand-list, p. 93. (Fig. 1, skull; fig. 2, animal.) Chelonia marmorata, Krauss, not Dumeril and Bibron. Hab. Ocean, French Guiana (Krauss). The palate deeply concave, with a deep well-marked groove on each side of the basioccipital bone, which has a very strong ridge on its front lateral margin. The alveolar surface of the upper beak with a very high arched ridge, which is much the highest in front, and very rugose on its edge and on the hinder part of its surface, having an obscure indication of a ridge parallel to its hinder margin, and then shelving down to the inner nostrils. The alveolar surface of the lower beak concave, very wide in front, narrow on the sides, becoming narrower behind, and with a sharp elevated ridge on the inner margin. There is a longitudinal central ridge across the hinder half of the concavity of the lower alveolar edge. The concavity of the alveolar of the lower jaw fits on to the ridge in the upper jaw. The inner surface of the beak within the hinder ridge is yellow and horny like the outer surface. It is broad and high in front, gradually narrowing on the sides ; the surface is smooth, with a groove on each side in the middle of the front; and the sides have close paralell grooves ending in crenations on the margin of the ridge. The specimen in the British Museum is full-grown, and has the dorsal shell 35 in. long, and 31 in. broad in the widest part over the |