PELECYPODA—PRIONODESMACEA. 



461 



Through the whole thickness of the Cretacic of Utah, Wyoming 

 and Colorado, and in the Dakota of Texas. 



Fig. 612. Ostrea soleniscus, X X A.- (After White.) 



Cretacic. 



264. 0. haydeni White. (Fig. 613.) 

 Small, usually not exceeding 2 inches in height. 

 Bear River: Wyoming, Idaho. 



265. 0. panda Morton. 

 Free margins of valves impressed with broad plications which 



do not extend to the beak. 



New Jersey (Marshalltown), Delaware, Texas (Coloradoan). 



Cretacic. 



Fig. 613. Ostrea haydeni. (After White. ) 



266. 0. congesta Conrad. (Fig. 614, c, d.) Cretacic. 

 Lower valve cup-shaped, with large area of attachment around 



which the shell margin abruptly bends up at a right angle. Upper 

 valve flat, with form of attached portion of lower valve. 



Very abundant in and characteristic of the Niobrara of North 

 America. Also occurs in the Benton. 



267. 0. lugubris Conrad. (Fig. 614, a, b.) Cretacic. 

 Varying from small to medium in size (breadth from -| inch to 



2\ inches). Plications 12 to 18 on each valve but developed only 

 around the margin of the upper valve. 



Kansas, Colorado (Niobrara-Pierre), New Mexico (Niobrara), 

 Texas (Eagle Ford-Navarro). 



