118 



CHELONIA. 



Genus CHRYSEMYS, Gray \ 



Neural bones of moderate length, with their antero-lateral surf aces 

 much shorter than the postero-lateral. Plastron extensively united 

 to the carapace by suture, with moderately long or short buttresses, 

 of which the inguinal is anchylosed to the 5th costal : humero- 

 pectoral sulcus placed entirely on the hyoplastral and considerably 

 behind the entoplastral bone. 



The vertebral shields are hexagonal and elongated; and the 

 pectoral shield is relatively short in proportion to the abdominal. On 

 the palate the oral surfaces of the maxilla are ridged. 



In provisionally referring the undermentioned Lower Eocene forms 

 to this genus the writer does so on the grounds that the above- 

 mentioned diagnosis (which in respect of the shell is taken almost 

 exclusively from the fossils) agrees precisely with that of the ex- 

 isting forms. If differences in the cranium be ultimately discovered, 

 then grounds would be available for the generic separation of the 

 Eocene forms. 



The existing representatives of the genus are exclusively American. 



Chrysemys testudiniformis (Owen 2 ). 

 Syn. Emys testudiniformis ; Owen 3 . 



Carapace much vaulted, without any trace of costal carina?. The 

 length of the carapace was probably about 0,305 (12 inches). 



Fig. 26. 



Chrysemys testudiniformis. — The imperfect plastron ; from the London Clay 

 of Sheppey. ^. ent.p, entoplastral bone ; hy.p, hyoplastral bone ; hp.p, 

 hypoplastral bone ; pec, pectoral shield ; ah, abdominal shield. 



1 Catalogue of Tortoises in Brit. Mus. p. 27 (1844). 



2 Kep. Brit. Assoc, for 1841, p. 161 (1842).— Emys. 8 Loc. cit. 



