149 



tering lateral teeth, near the hinge, 

 cardinal pits. 



Ligament internal, inserted in the 



2. Shells not gaping at the sides. 



Crassatella. Shell inequilateral, suborbicular or transverse; the valves 

 close; two rather diverging, cardinal teeth, and a pit by the side of them. 

 Ligament internal, inserted in the pit of each valve; lateral teeth, none; or 

 obsolete. 



C. Kingicola, 

 ' donacina, 

 ' sulcata, 



C. rostrata, 

 ' glabrata, 

 ' subradiata, 



C. contraria, 

 ' cuneata, 

 ' erycinsea, 



C. cycladea, 

 ' striata. 



Erycina. Shell transverse, rather inequilateral, equivalve, rarely gaping; 

 two unequal, diverging, cardinal teeth, having a pit between them; and two 

 oblong, compressed, short, entering, lateral teeth. Ligament internal, fixed 

 in the pits. 



E. cardioides. 



DIVISION II. Ligament showing itself on the outside, or being double; 

 has one internal, the other external. 



Ungulina. Shell longitudinal or transverse, rounded on the upper part, 

 subequilateral; valves not gaping, beaks eroded. A short and rather bifid 

 cardinal tooth in each valve; with an oblong, marginal, adjoining pit, divided 

 in two by a contraction. Ligament internal, inserted in the pits. 



U. oblonga, U. transversa. 



Solenimya. Shell equilateral, equivalve, transversely oblong, the ex- 

 tremities obtuse; the epidermis shining, and extending beyond the margin. 

 Beaks not prominent, scarcely distinct. One cardinal tooth in each valve, 



