II06 CLASS REPTILIA. 



Cinosternum by the presence of eight neural bones, and the long 

 bridge connecting the carapace with the plastron. 



Family Dermatemydid/e. — The genus Dermatemys, of Central 

 America, is taken as the type of a family which includes Stauro- 

 typus of the same region, and in some respects connects the 

 Cinosternidce. with the Chelydridce. The nuchal bone has a costi- 

 form process, as in both those families ; the temporal fossae of the 

 skull are not roofed over ; the caudal vertebrae are procoelous ; and 

 in the pelvis the pubis and ischium of the same side do not unite 

 to enclose an obturator foramen. The shell is well ossified, but in 

 the type genus the union between the costals and marginals does 

 not take place till a late period. Baptemys, of the Upper Eocene 

 of North America, which has been included by Professor Cope in 

 Dermatemys, is distinguished from the latter by having the full 

 number of neural and suprapygal bones, so that none of the costals 

 meet in the middle line. Here may be mentioned several allied 

 North American forms, most of which are referred by Professor 

 Cope to a distinct family — the Adocidce — mainly on account of the 

 circumstance that the ribs do not develop heads to articulate with 

 the vertebrae ; but since the same feature occurs in Testudo 

 among the Testudinidce, it cannot be regarded as of family value. 

 In Homorophus, of the American Cretaceous, there is no inter- 

 gular shield, and the vertebral shields are very narrow. In Adocus, 

 of the Upper Cretaceous, and Agomphus (with which Dr Baur states 

 Amphiemys is identical), of the Eocene, intergular shields were 

 present. The former has traces of sculpture on the shell ; while in 

 the latter the epidermal shields are very thin, and the surface of the 

 shell is marked with a faint vermiculate sculpture. We are thus led 

 on to the European Trackyaspis, which is probably an allied form, 

 and with which one or other of the American types may perhaps 

 prove to be identical. This genus, which has elongated vertebral 

 shields recalling those of Dermatejnys and Baptemys, occurs typically 

 in the European Tertiary, and has also been recorded from the 

 Lower Greensand of Switzerland, although the latter form has been 

 referred by Professor Riitimeyer to Plesiochelys. A nearly entire 

 carapace has also been obtained from the Tertiary of Egypt. The 

 surface of the shell is covered with a distinct vermiculated sculpture 

 like that of Trionyx, but thin epidermal shields were present. 



Family Platysternid^e. — The existing Burmese genus Platy- 

 sternum is represented by a very small Chelonian forming the only 

 member of a family which connects the Chelydridce with the Testu- 

 dinidcE. Thus the temporal fossae of the skull are roofed over, the 

 pelvis is of a Chelydroid type, and the caudal vertebrae are mostly 

 opisthoccelous ; but the nuchal agrees with that of the Testudinidce 

 in having no costiform process. 



