79 



O S T R E A. 



A. Valves furnished with ears^ and radiate; 



Pecten, 



1. Equilateral; ears equal. (Plate IX. fig. 1.) 



2. Ears unequal, (fig. 2.) 



S. Valves more gibbous on one side; hinge 

 rather oblique ; ears short, (fig. 3.) 



B. Rough, and generally plated on the outside. 



(fig. 4.) 



C. Hinge with a perpendicular grooved line. 



(fig. 5.) 



Shell generally inequivalve, more or less eared. 

 Hinge without teeth, having a hollow cavity or 

 sinus, and in many instances lateral transverse 

 grooves or furrows. 



Shape of the pectinated division orbicular, at- 

 tenuated towards the hinge, eared ; of the other 

 divisions orbicular, lobed, or produced towards the 

 apex. Much as the divisions A and B do vary 

 from each other, there seems more generic affinity 

 between them than is usually admitted. The ani- 



