PELECYPODA—PRIONODESMACEA, 



471 



Differs from G. convexa in absence of sulcus and in smooth 

 surface. 



Washita of Mexico. Cretacic : Delaware, Texas and Mexico 

 and west to Montana. Also Europe. 

 292. G. mutabilis Morton. (Fig. 628.) Cretacic. 



Lower valve depressed-convex and comparatively thin. 



Fjg. 627. Gryphcea vesicularis. Lower and upper valves. (Md. Surv. 



Especially characteristic of Marshalltown of New Jersey. 

 293. G. convexa (Say). (Fig. 629.) Cretacic. 



Lower valve with posterior ear separated from the rest of the 



FlG. 628. Gryphcea mutabilis. (N. J. Pal., I. 



