PELECYPODA—TELEODESMACEA. 561 



552. P. lenis Conrad. (Fig. 769.) Eocenic. 



Fig. 769. Protocardia lenis, right valve. (Md. Surv.) 



Posterior margin oblique. Radiating lines about 22. 

 Pamunkey of Maryland, Virginia, Alabama (Lignitic). 



CLIX. Isocardia Lamarck. 



Inflated, smooth or concentrically striated. Beaks distant, 

 prominent and much produced and spirally enrolled toward the 

 front. Each valve with two nearly parallel cardinal teeth and one 

 posterior lateral. Jurassic-Recent. 

 553. I. cliffwoodensis Weller. Cretacic. 



Ventricose (convexity of valves 6.5 mm.). Beaks small, 

 strongly incurved and directed forward. Anterior umbonal slope 

 abrupt ; posterior slope convex. Surface smooth. 



Ripleyan of New Jersey (Cliffwood-Wenonah), Texas. 



FlG. 770. Isocardia fraterna, right and left valves, X Vi- (Md. Surv.) 



554. I. fraterna Say. (Fig. 770.) Miocenic. 



Surface crossed by rather large concentric wrinkles. 

 Maryland-North Carolina. 



