PLATE XLI. 



PAGE 



Figs. 1-8. Ceassatellites alaeformis (Conrad) 180 



1. Exterior of the right valve of the type specimen of C. decUvis 



Heilprin. Aquia Creek. U. S. National Museum. (After 

 Aid rich.) 



2. Exterior of the left valve of the same. (After Aldrich.) 



3. Exterior of right valve. Fort Washington. 

 3a. Interior of the same. 



4. Interior of left valve. Fort Washington. 

 4a. Exterior of the same. 



5. Exterior of left valve. 



6. Exterior of left valve. Fort Washington. 

 6a. Interior of the same. 



7. Interior of left valve. Fort Washington. 

 7a. Exterior of the same. 



8. Exterior of right valve. Fort Washington. 

 8a. Interior of the same. 



393 



