GENERA OF SHELLS. 23 



(b.) Internal margin crenulated or toothed. 

 D. ringens, rugosa, Caienensis, elongata, denticulataj car- 

 dioides, rneroe, scripta, Irunculus, fabagella, anatinura, mar- 

 tinicensis, variabilis, fossor. 



II. Having no lateral teeth. 



Capsa. Shell transverse, equivalve, closed. 

 Hinge with two teeth in the right valve, em- 

 bracing a bifid tooth in the other ; lateral teeth 

 none ; ligament exterior, on the short side. 



The capsœ are rather inequilateral shells, allied to 

 the psammobife and certain tellinse by their cardinal 

 teeth, but they scarcely gape at the side, and have not 

 tlie flexuous fold of tellina. 



C. laevigata, Brasiliensis. 



Crassina. Shell suborbicular, transverse, 

 equivalve, sub-inequilateral, closed. Hinge with 

 two strong diverging teeth on the right valve, 

 and two very unequal teeth on the other ; lig- 

 ament exterior, on the longer side. 



The crassina resembles a small crassatella in appear- 

 ance, solidity and perfect closeness when shut, but dif- 

 fers in the position of the ligament. It differs from 

 venus by having only two teeth on each valve, those of 

 the left appearing almost like a single tooth, one of 

 them being large, and the other but very shghtly prom- 

 inent. 



C. Danmoniensis. 



