Cope.l J-*" [Dec. 16, 



III. Plastron uniting with, the marginal bones of the carapace by straight 

 contact only. (Feet ambulatory. ) Lysostema. 

 No intersternal bone nor intergular scutum ; a mesosternal bone and three 



series of phalanges Cistudinidce. 



The extinct species of the Cryptodira of this continent belong to eight of 

 the above families. I give diagnoses of the genera to which they are 

 referred. Names of existing genera are in Roman type. 



Cheloniid^e. 



Postabdominal bones distinct from each other .Chelonia Brong. 



Postabdominal bones united with each other by suture. .Pwppigerus Cope. 



Propleurid^j Cope.* 

 Transactions of American Philosophical Society, xiv., 1870, p. 235. 

 Ten costal bones ; first two marginals united with carapace by suture ; 



shell smooth, flattened Osteopygis Cope. 



Nine costal bones ; first two marginals united to carapace by suture ; shell 



sculptured (a high dorsal keel) Peritresius Cope. 



Nine costal bones ; one marginal united with carapace by suture ; second 



by costal gomphosis ; shell not keeled nor sculptured 



Propleura Cope. 

 1 Nine costal bones ; first united with carapace by suture ; second without 



costal gomphosis ; shell not sculptured Catapleura Cope. 



? Nine costal bones ; marginals all free ; shell not sculptured 



Lytoloma Cope. 

 Trionychid^e. 



a. Surface of bones smooth. 

 Postabdominal suture digitate Axestus Cope. 



aa. Surface of bones sculptured. 



/?. Sutures of plastron digitate. 



A dermal flap protecting posterior legs below ; marginal bones 



Emyda Gray. 



A dermal flap ; no marginal bones Cyclanosteus Peters. 



No dermal flap nor marginal bones ; muzzle much abbreviated 



Chitra Gray. 

 No dermal flap nor marginal bones ; muzzle elongate. . . .Trionyx Geoffr. 



/?/?. Suture for postabdominal coarsely serrate. 



Postabdominal recurved in front Plastomenus Cope. 



# 



Chelydridjs. 

 a. Bridges of plastron wide ; ? caudal vertebrae. 



One row of marginal scuta ; six pairs of scuta of the plastron 



Idiochelys Myr. 



* Palceochelys novemco status Geoffr., belongs to this family, but not Palmo- 

 chelys Myr. 



