PELECYPODA—PRIONODESMACEA. 



439 



205. G. propleura (Meek). (Fig. 577.) Cretacic. 



More or less oblique. Right valve flat, smooth, without a 

 byssal notch. 



Colorado (Benton), Utah (Coloradoan), Georgia (Ripleyan). 



Fig. 577. Getvillia propleura, left valve. (After Stanton, Bull. 106, U. S. G. S.) 



LXVI. Gervilliopsis Whitfield. 



Differs from Gervillia in the absence of teeth on the posterior 

 portion of hinge and the oblique dental ridges below the ligament 

 area on the posterior end. It also differs in the truncation of the 

 anterior end, in the continuation of the ligamental (striated) area 

 along the anterior truncation, and in the gaping of the valves 

 anteriorly. Beaks terminal. Comanchic-Cretacic. 



206. G. invaginata White. Comanchic. 



Curved, marked by a central ridge running down its entire 

 length midway between the margins. Hinge line with about 12 

 ligament pits. 



Upper Washita of Texas. 



