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Show 1869.] DR. J. E. G R A Y O N T H E T O R T O I S E S . 223 gans the spots on the crown are small and those on the sides of the head are larger and unequal-sized. III. THE SEA-TURTLES-CHELONIA. The common Turtle, covered with horny plates, has a skull as different from that of the coriaceous Turtle, which has the bones of the body covered with a soft skin, as the two animals are different in external appearance. I formerly regarded the coriaceous and the scale-bearing Turtles as forming two distinct families (Annals of Philosophy, 1825, vol. x. p. 212); but having received from Mr. Collie, as stated in the ' Catalogue of Shield Reptiles,' a skull of a true Chelonian as that of a coriaceous Turtle (Sphargis), and finding they were so much alike, I was induced to reconsider the question and to unite Sphargis and Chelonia in the same family, regarding them as distinct tribes characterized by the nature of the surface. Such a mistake was excusable, as I a m not aware that the skull of the adult Sphargis is in any European collection, or has ever been figured, and I had overlooked the figure of the skull of the very young specimen that is given in Prof. John Wagler's ' N e w System of Amphibia,' t. 5. f. 1. In that work the skulls of the young Chelonia and young Sphargis are figured side by side ; therefore the distinction can be easily seen. The great peculiarity of the skull of the genus Sphargis consists of the opening to the nose being in the upper part of the head, the nose-cavity being carried up by the elongated erect form of the intermaxillary bone; the orbits are also exceedingly large. Fam. T. CHELONIADAE. Cheloniadee, Gray, Ann. Phil. 1825, x. p. 212. The thorax covered with distinct horny plates; the sterno-costal suture covered with a longitudinal series of sterno-lateral plates. Nose anterior, erect; the nostrils anterior, at the upper edge of the nose. Upper jaw simple, or rather hooked in front. Eyes moderate. Skull oblong, crown flat behind; orbit moderate, nose truncate, erect; nostrils anterior, on the upper part of the nose. The intermaxillary bone small, narrow, short, erect. The study of the skulls of these animals first led me to observe the importance of the alveolar chewing-surface of the jaws for distinguishing the genera. The Turtles may be divided into two groups thus:- * The alveolar surface of the upper jaw concave, broad, narrower behind, with a single linear central ridge. Lower concave, with a rather strong ridge on the inner side. Carnivorous. 1. CARETTA. |
