PELECYPODA—PRIONODESMACEA 



463 



with strong concentric undulations. Internal mold nearly smooth. 

 Height about 2 inches ; greatest width about 1 J inches. 



Ripleyan of New Jersey (Wenonah), Georgia, Texas. 

 271. 0. falcata Morton (<9. larva of American authors). (Fig. 616.) 



Cretacic. 



Lower valve moderately convex with small scar of attachment. 

 Upper valve flat. Plications alike on both valves. 



Fig. 616. Ostrea falcata Morton. (After Whitfield, Pal. N. J., I.) 



New Jersey (very abundant in Marshalltown ; also in Navesink), 

 Arkansas. 



272. 0. mesenterica Morton. Cretacic. 

 Smaller than O. falcata and with non-plicate central area. New 



Jersey (very abundant in Navesink ; also in Red Bank and Tinton). 



273. 0. nasuta Morton. Cretacic. 



FlG. 617. Ostrea plumosa Morton. (N. J. Pal., I.) 



Central portion non-plicate as in O. mesenterica, from which it 

 differs in large size and broader plications. 



New Jersey (Red Bank and Tinton ; sparingly in Navesink), 

 Texas. 

 274. 0. plumosa Morton. (Fig. 617.) Cretacic. 



