124 MOLLUSC A. 



No. 350. Ostrea, 



From the Petrified Forest, Nunimulitic Eocene, near Cairo, Egypt. 



No. 351. G-ryphea arcuata, Lam. (Gryphea incurva, Sow.) 



This genus, belonging to the Oyster Family 

 (Ostreidse), is exclusively Mesozoic; 30 species 

 known. The left valve has a prominent incurved 

 umbo. From the Lias, Lyme-Regis, England. 



No. 352. Gryphea vesicularis, Lam. 

 Upper Cretaceous, Marlborough, N. J. 



No. 353. Exogyra arietina, d'Orb. 



In this member of the Oyster family, also restricted to the Cretaceous, the 

 beak is reversed or turned posteriorly. From the Cretaceous, Griffith Ravine, 

 Texas. 



No. 354. Exogyra costata, Say. 

 From the Greeusand, Marlborough, N. J. 



