PELECYPODA—PRIONODESMA CEA . 



421 



159. P. (Cornellites) flabellum (Conrad). (Fig. 551.) Devonic 

 Left valve with beak curving to or over the hinge margin. Sur 

 face marked with 6-12 strong ribs alternat- 

 ing with one to several weaker rays, the 

 latter present also on the ears. Right 

 valve with beak depressed, not rising above 

 the hinge ; surface lacking rays except 

 weak ones on the posterior ear. Both 

 valves crossed by concentric growth lines. 

 Characteristic of the Onondaga and 

 Hamilton of New York to Indiana, Michi- 

 gan, Ontario and the Appalachian region ; also rarely in the Che 

 mung Group of the same region. 



Fig. 549. Pterinea navi- 

 formis, left valve. (Pal. N. 

 Y., III.) 



Fig. 550. Pterinea gebhardi, X h (After Hall, Pal. N. Y., III. ) 



160. P. chemungensis (Conrad). (Fig. 552, a, b.) Devonic. 



Surface of left valve marked with slender, interrupted, irregularly 

 alternating rays which on the right valve are confined to the ears. 

 Surface of both valves crossed by fine concentric striae. Valves 

 are often less oblique than in figure. 



Chemung Group : New York. 



