PLATE XX, 



Ostrca congcsta, Conred. 

 Fig. I. Interior of right valve. 

 Fig. 2. Exterior view of right valve. 

 Fig. 6. Interior of left valve. 



Modiola. sp. 

 Fig. 4. Exterior of right valve. 



Oitrca twcgyro nil's, 11. s/>. 

 Fig. 3. Interior of left valve. 



Corbula, sp. 

 Fig. 5. Interior of one valve. 



Ostrca wcllcrii, n. sp. 

 Fig. 7. Interior of right valve. 

 Fig. 8. Exterior of left valve. 



Ostrea kaiisasciisis, n. sp. 

 Fig. 9. Exterior of left valve. 

 Fig. 10. Exterior of left valve. 

 Figr II. Interior of left valve. 



