145 



[Cope. 



One row of marginal scuta ; scuta of plastron ? not distinct 



Hydropelta* Myr. 



aa. Bridges of plastron very narrow. 



/9. Carapace smooth, not sculptured. 



Two I'ows of marginal scuta ; five pairs of scuta of the plastron 



Macrochelys Gray. 



One row of marginals ; five pairs on plastron Chelydra Schw . 



One row of marginals ; four pairs of scuta on plastron .... Claudius Cope. 



/9/?, Carapace sculptured. 

 One row of marginal scuta Anostira Leidy. 



Baenid^. 



Cope, Annual Report U. S. Geol. Surv. Terrs., 1872 (1873), p. G21. 



Supramarginal scuta (Riitimeyer) ; no interhumerals Platychelys Myr. 



No supramarginals nor interhumeral scuta Baena Leidy. 



No supramarginals ; interhumeral scuta present Polythorax \ Cope. 



ADOCIDiE. 



Cope, Proceedings American Philosophical Society, 1870, p. 559. 

 a. Vertebral bones and scuta normal. 



One intergular scutum entirely separating the gulars Adocus Cope. 



Either two iutergulars, or the gulars meeting behind intergular 



Amphiemys Cope. 

 aa. Vertebral bones wedge-shaped, widening upwards ; vertebral 

 scuta not wider than the bones. 

 Elements of carpace early coossified Homorhophus Cope. 



Emtdid.e. 



a. No scutal sutures. 

 Surface sculptured Apholidemys Pom. 



aa. Scuta including intermarginals and two anals. 



Lobes of sternum narrow Dermatemys Gray. 



Lobes of sternum wide Arjomphus Cope. 



aaa. Scuta ; two anals, no intermarginals. 



Surfaces of carapace sculptured; plastron fixed Compsemys Leidy. 



Surfaces of carapace smooth ; plastron fixed ; recent Emydidce and the 



genus Emys Brong. % 



Posterior lobe of plastron movable ; surface smooth Ptychogaster Pom. 



Anterior and posterior lobes of plastron movable ; surface smooth 



DUhyrosternum Pict. et Humb. 



aaaa. Scuta ; one anal, no intermarginals. 

 Carapace smooth Stylemys Leidy. 



* Eurysternum Wagn. (Palceomeclicsa et Acichelys Myr. (fide RUtimeyer) is 

 nearly allied to Hydropelta.) 



t Possibly one of the Adocidce ; see Proceed. Acad. Phila., Oct., 1876. 



X Gray has distinguislied several good genei-a among existing sijecies on 

 cranial characters. 



