EXPLANATION OF PLATE XL 

 Mercenaria Ducateli Conrad (p. 67). 



Figs. 1,2. Exterior of the type specimen of the species and the hinge of the same. The remainder 

 of the shell is filled with shell rock which could not he removed. 

 3. View of another fragment preserving the surface features. 

 4, 5. Exterior and interior of an elongated specimen referred to this species with doubt. 



6. Anterior view of the valves in conjunction, showing the general form. 



7. Interior of a short form which presents the same, kind of surface as fig. 4. 



166 



