942 GIBBOSULA 
rather high; beak sculpture not seen; posterior two-thirds of 
the shell covered with somewhat radiating corrugations and 
nodules; posterior slope having strong, subradial folds; epi- 
dermis dark ; hinge plate very wide; pseudocardinals not large, 
stumpy, rough; laterals very heavy, club shaped; beak cavities 
enormously deep and compressed; anterior cicatrices rather 
shallow, rough in the bottom; posterior cicatrices deep and 
distinct; a strong rib runs from the front part of the beak 
cavity toward the posterior base; nacre whitish. 
Animal unknown. 
Type, Mya crassa Wood. 
GIBBOSULA CRASSA (Wood). 
Shell somewhat elongated, convex, subtriangular, inequi- 
lateral, ponderous; beaks rather low, but the umbonal region 
elevated; posterior ridge well developed, narrowly rounded, 
not so full as the region in front of it; anterior end rounded ; 
base nearly or quite straight; outline of dorsal slope curved, 
ending behind in a point at the termination of the posterior 
ridge, the region between this and the base obliquely subtrun- 
cated; surface with rude, concentric growth lines; the hinder 
three-fifths of the shell covered with broken, subradial ridges, 
which are divaricate just in front of the posterior ridge; epi- 
dermis brown; hinge very heavy, the plate flattened ; pseudo- 
cardinals low, somewhat ragged; laterals remote, short, solid, 
that of the right valve partly double; muscle scars deep; beak 
cavities very deep, compressed; nacre white or flesh-colored, 
thick in front with an oblique rib running downward and for- 
ward from the pseudocardinals, an oblique furrow near the 
laterals, and having numerous small scars, by which the mantle 
is attached to it. 
Length t10, height 71, diam. 40 mm. 
China. 
Mya crassa Woop, Gen. Conch., 1815; p. 106, pls.) xx, xxi; 
Ind. Test., 1825, p. 12, pl. 11, fig. 28b ; Ind. Test. Rev., 1856, 
Ds 10.) ple nie es 28. 
Gibbosula crassa StMPSON, Syn.. 1900, p. 804. 
Mya ponderosa.Dituwyn, Dill. Cat., I, 1817, p. 5. 
