1869. | DR. J. E. GRAY ON THE TORTOISES. 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 find- 
ing they were so much alike, I was induced to reconsider the ques- 
tion and to unite Sphargis and Chelonia in the same family, regard- 
ing them as distinct tribes characterized by the nature of the surface. 
Such a mistake was excusable, as I am 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 ‘ New 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. I. CHELONIAD. 
Cheloniade, 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 inter- 
maxillary 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 distin- 
guishing 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. 
