286 DIMYARIA.—SOLENID&. 
GENUS SOLEN. 
The characters already enumerated belong pre- 
eminently to this, the principal genus; one or 
two others which are associated with it presenting 
them with less distinctness and with more approx1- 
SOLEN. 
mation to the neigbouring families. The hinge is 
usually composed of a well-defined cardinal tooth 
and a lateral fulcrum in each valve. It varies in 
position. The hinder muscular impression is ob- 
