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DIMYARIA.—SOLENIDÆ.
Genus Solen.
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 approximation 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-