EXPLANATION OF PLATE XI. 

 Mercenaria DucATELi C'oiirad (p. 67). 



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

 of the sliell is filled with shell rock which could not be 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. 



(!. 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 



