PLATE XXI, 



Ostrca ellsworthetisis, ?i. s/>. 

 Fig. I. Interior of left valve. 

 Fig. 2. Exterior of left valve. 



Ostrea canonensis, ?i. sp. 

 Fig. 3. Exterior of left valve. 

 Fig. 4. Interior of left valve. 



Ostrca tvillistonii, 11. sp. 

 Fig. 5. Interior of left valve. 

 Fig. 6. Exterior of left valve. 



Ostrca crenula, n. sp. 

 Fig. 7. Exterior of right valve. 

 Fig. 8. Interior of right valve. 

 Fig. 9. Exterior of right valve. 



Ostrea led, n. sp . 

 Fig. 10. Exterior of right valve. 

 Fig. II. Interior of right valve. 



