QUADRULA 909 
nected, torn pseudocardinals and two curved, heavy laterals, 
the lower larger; right valve with two pseudocardinals, the 
lower very large, the upper long and compressed and one 
strong lateral with a vestige of another above and a third be- 
low it; beak cavities very deep, not compressed; dorsal scars 
in a long row under the pseudocardinals; muscle scars deep, 
the anterior ones very rough; pallial line distant from the bor- 
der in front; nacre rose-colored to deep coppery-purple, very 
much thickened in front. 
Length 82, height 70, diam. 55 mm. 
Guatemala in the Usumacinta River; Tabasco, Mexico. 
Unio usumasinte Crossr and Fiscrer, J. de Conch., XL, 1892, 
p. 294.—-Fiscurr and Crosse, Miss. Sci., I, 1894, p. 574, 
piss Perino 4 5 Lxvit, fig, 5: 
Ouadrula usumasinte SIMPSON, Syn., 1900, p. 796. 
The specimen figured by Fischer and Crosse is young and 
has a pink nacre. I have seen a fine adult specimen of what 
is undoubtedly this species, which is one of the most robust 
in the development of its parts of any Naiad | know of. It is 
larger, more inflated, and solider than Q. ostreata. 
QUADRULA GUATEMALENSIS Simpson. 
Shell subrhomboid, longer than high, inequilateral, subcom- 
pressed, subsolid, with moderately high, but not swollen, beaks, 
whose sculpture is eroded in the only specimen seen; anterior 
end narrowed, subangular, rounded in front; posterior ridge 
low, double, ending in a feeble biangulation behind at the base* 
of the shell; surface with rather close, irregular, nodulous, con- 
centric sculpture; epidermis brown, lighter behind, rayless; 
left valve with two subcompressed pseudocardinals and one 
lateral with a vestige of another above it; right valve with a 
ragged pseudocardinal and one curved lateral; beak cavities 
only moderately deep; anterior muscle scars impressed; pos- 
terior scars shallow; nacre coppery-purple, slightly iridescent 
behind, thicker in front. 
Length 45, height 28, diam. 14 mm. 
Rio Usumacinta, Guatemala. 
