22 PROCEEDINGS OF THE ACADEMY OF 



SYNOPSIS OF THE SPECIES OF THE CHELYDEIN^. 

 BY E. D. COPE, A.M. 



This group of tortoises, so far as their structure is exactly 

 known, is confined to North and Tropical America. The number 

 of species is small, though the present list adds several to those 

 previously known. Their structure is highly interesting, as ex- 

 pressing relationship to groups which existed during mesozoic 

 time. I allude to the family of Propleuridae, found in the creta- 

 ceous greensand of New Jersey, which possessed features of the 

 sea-turtles, combined with those of the present group, or the 

 snappers. The latter possess the imperfect and small plastron 

 of the Propleuridse, conjoined with the ambulatory limbs of the 

 Emydidse. In other respects they resemble the Emydidee, and 

 I am inclined, until further discoveries of structural peculiarities 

 shall have been made, to allow them to remain in that family, 

 although both Dr. Gray and Prof. Agassiz have referred them to 

 a distinct one, under the name of Ghelydidee. Certain it is, that 

 they are also related to the Cinosternidse, which is peculiar in the 

 absence of the mesosternal bone. Claudius approaches the latter 

 family in its short tail and lack of posterior vertebral bones. 



The only possible exception to the rule of distribution above 

 laid down, is the genus Platysternum, Gray, from eastern Asia. 

 This form has been placed here, but appears to associate them 

 with more typical Emydidse; until its structure be better known, 

 its position will remain doubtful. 



The vertebrae of Chel ydr a serpentina present some peculiarities 

 as compared with Trionyx Testudo and Emys, as follows: 



Testudo polyphemus. Cervical vertebrae 2-3 and 4 opisthocoelian, 4th bi- 

 convex, remainder procoelian. Caudal vertebra? all proccelian. 



Trionyx ferox. Cervical vertebra all opistkoccelian, caudals all proccelian. 



Chelopus guttatus. Cervical vertebrae as in Testitdo, the balls of the poste- 

 rior transverse bilobed ; caudals all procoelian. 



Chelydra serpentina. Cervicals as in Testudo ; the caudals all opisthocoelian. 



There are only three well-ascertained genera of this family, to 

 which a fourth may perhaps be added. Thej r are distinguished 

 as follows : 



[April 10, 



