Cope.l 144: jDpc. 16, 



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

 contact only. (Feet ambulatory.) Lysosterna. 

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



series of phalanges OistudinidcB. 



The extinct species of the Cryptadira 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^. 



Postabdominal bones distinct from each other Chclonia Brong. 



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



Propleurid^ Cope.* 

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

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

 shell smooth, flattened Osteopygis Cope- 

 Nine costal bones ; first tw^o marginals united to carapace by suture ; shell 



sculptured (a high dorsal keel) Peritredus Cope. 



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



by costal gomphosis ; shell not keeled nor sculptured 



Proplcura Cope. 

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



costal gomphosis ; shell not sculptured Oataplenra Cope. 



tNine costal bones ; marginals all free ; shell not sculptured 



Lytoloma Cope. 

 Trionychid^. 

 a. Surface of bones smooth. 



Postabdominal sutui'e digitate Axestus Cope. 



aa. Surface of bones sculptured. 

 jS, Sutures of plastron digitate. 



A dermal flap protecting po.sterior legs below ; marginal bones 



Em3'da Gray. 



A dennal flap ; no marginal bones Cyclanc^teus Peters. 



No dermal flap nor marginal bones ; muzzle much abbreviated 



Chitra Gray. 

 No dermal flap nor marginal bones ; muzzle elongate. . . .Triony.x Geoff"r. 



/9^3, Suture for postabdominal coarsely serrate. 

 Posta'bdominal recurved in front Pla&toincnus Cope. 



CUELYDRID^. 



a. Bridges of plastron wide ; ? caudal vertebi-a). 



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



Idiochclys Myr. 

 * Pal(Bochelys novemcostatus Geoffr., belongs to this family, but not Palceo- 

 ehelys Myr. 



