CUNEOPSIS 943 
Margarita (Unio) ponderosus Lea, Syn., 1836, p. 14; 1838, p. 
14. 
Unio ponderosus Hanyey, Test. Moll., 1842, p. 177. 
Margaron (Unio) ponderosus Les, Syn., 1852, p. 21; 1870, p. 
22: 
A remarkable Naiad of whose systematic position I cannot 
be certain. Its general form is something like that of a very 
heavy Afargaritana and the numerous small pits by which in 
life the mantle is attached to the nacre carry out this resem- 
blance. But the shell is exceedingly ponderous, the hinge plate 
is wide and flat, the teeth are well developed and Ouadrula-like, 
as are the very deep, compressed beak cavities. The oblique 
rib and furrow in the cavity of the shell recall Unio gibbosus 
or some of the Ptychobranchi. 
Genus CUNEOPSIS Simpson, 1900. 
Cuneopsis SIMPSON, Syn., 1900, p. 804. 
Shell solid, elongated, wide and truncate or rounded in front, 
tapering to a point behind; often twisted on its axis and curved 
to the right or left; beaks rather high, anterior; beak sculp- 
ture apparently a few coarse, subparallel, nodular ridges curved 
up behind; posterior ridge low, close to the hinge line and in 
front of it the shell is full; surface slightly, irregularly, con- 
centrically striate; epidermis dark, having a peculiar, dull, 
silky luster; hinge rather narrow; pseudocardinals two in the 
left valve immediately under the beak, the anterior com- 
pressed, high and nearly parallel with the outer edge of the 
shell, the posterior heavy, joined to the anterior above, with 
a deep, triangular cavity between; right valve with one large, 
triangular, anterior pseudocardinal with a deep, triangular pit 
back of it, and often a small, low, compressed tooth behind the 
pit; laterals granularly striate; beak cavities rather deep; an- 
terior muscle scars deep, rough at the bottom; posterior scars 
large, long and oblique; nacre silvery, sometimes radially 
striate at the edge; pallial line indented into a sinus at its 
posterior end, above which is a granular, striate callus. 
Animal unknown. 
Type, Unio celtiformis Heude. 
