378 FOSSIL OSTREID^ OF NORTH AMERICA. 



PLATE LVI. 



ExoGYRA COSTATA Say. (Page 301.) 



Fig. 1. — Lateral view of a lower valve; natural size. 



2.— Exterior view of au upper valve. For other figures of this species see Plate 

 LVII. 



ExoGTKA ARIETINA Kocmcr. (Page ^03. ! 



3.— Lateral view of a large lower valve, with the heak uuiisuallv long ; natural 



size. 

 4. — A smaller example, showing the upper valve in phico. 

 5. — Lateral view of the same example. 

 6, 7. — Copies of Say's ligures o£ Delphi iiul a laxa for compaiison with E. arietina. 



