464 



NORTH AMERICAN INDEX FOSSILS. 



Thin. Sometimes faintly plicate. Upper valve marked with 

 fine radiating striae which diverge from a median line. 



New Jersey (Marshalltown-Red Bank), Virginia, Gulf region, 

 Wyoming (Montana). 



275. 0. bryani Gabb. Cretacic. 

 Somewhat like Gryphcea convexa but with evidence of attach- 

 ment of convex valve and with beak not strongly incurved. 



New Jersey (Vincentown and Manasquan). 



276. 0. glabra Meek and Hayden. (Fig. 618.) Cretacic. 



Fig. 618. Ostrea glabra. Upper and lateral view of a nearly complete shell, 

 Xk- (After White.) 



Subovate, sometimes slightly arcuate laterally. Beak of lower 

 valve curved to the right ; cardinal area small and deep. Surface 

 of both valves entirely free from radiating plications or projecting 

 concentric lamellae, though there are obscure striae and a few faint 

 growth ridges. Size 3 inches x 1-^ inches. 



Laramie : Colorado, Montana, Alberta. Fox Hills : Wyoming. 

 Pierre : Montana, Assiniboia. Also San Luis Potosi. 



277. 0. subtrigonalis Evans and Shumard. Cretacic. 

 Small, depressed, narrowly ovate, slightly arcuate laterally. 



Lateral margins of lower valve crenate. Upper valve nearly flat. 

 Surface of each valve marked with concentric striae and furrows. 

 Height not quite 2 inches; width not quite 1 inch. 



Pierre : Montana, Alberta, Assiniboia. Livingston : Montana. 



278. 0. inornata Meek and Hayden. Cretacic. 

 Small, subovate, thin, attached by whole under side of lower 



valve. Beaks pointed and bent laterally. 



