PELECYPODA—PRIONODESMACEA. 



469 



Kansas, Oklahoma, New Mexico, Texas. 

 287^. G. corrugata var. belviderensis Hill and Vaughan. 



Comanchic. 



Large but differs from tucumcarii in its more triangular and 

 flattened outline. 



Comanchic of southern Kansas and Texas. 



Fig. 624. GryphcEa corrugata. Exterior and interior of lower valve, X 2 A- 

 (After Hill and Vaughan.) 



288. G. navia Hall. (Fig. 625, d, e.) Comanchic. 

 Lower valve distinguished from G. corrugata which it resembles 



in beak and surface characters, by its smaller size, the possession 

 of a dorsal carina separated from the dorsal sinus by a depressed 

 area which at times is marked by slight ridges and by having a 

 dorsal wing, produced by the expansion of the valve at the margin. 

 Characteristic of the Washita from Kansas to Mexico. Ex- 

 ceedingly abundant in the Kiamitia clays of Texas and Oklahoma. 



289. G. washitaensis Hill. (Fig. 625, a-c .) Comanchic. 

 Thin. Lower valve with well developed wings on both sides. 



Growth lines fine. 



Characteristic of the middle Washita of Texas, usually asso- 

 ciated with Ostrea carinata and occurring in great sheets. 



290. G. mucronata Gabb. (Fig. 626.) Comanchic. 

 Similar to G. marcoui but larger, heavier, and with less abruptly 



constricted beak. The dorsal sinus begins farther up the umbo 

 than in G. marcoui and the growth lines are coarser. 



