49 



S O L E N. 



(See Plate IV. Fig. 4 and 5.) 



Shell oblong, gaping at both ends. Tooth of 

 the hinge subulate, reflex, often double, not in- 

 serted. (Fig. 3.) Lateral margin obsolete. 



The valves are convex, and in some of the more 

 oval species, the beaks, which are mostly obsolete, 

 are short and incurved. 



In a few species there is an internal rib extend- 

 ing from the hinge to the margin of the cavity in 

 a longitudinal direction. The disproportionable 

 breadth of the shells in this genus is a remarkable 

 character, and many of them are extremely 

 brittle. 



The form of the solen is extremely well adapted 

 to the motions of the animal which it contains ; 

 these being exclusively in a perpendicular direc- 

 tion. It makes ' its way through the sand of the 

 sea-shore, to a certain depth, and thence again 

 to the surface to seek for food. This is a tribe 

 which can hardly be confounded with any other. 



