908 QUADRULA 
curved behind; surface covered with strong, irregular, con- 
centric, nodulous ridges; epidermis greenish-brown, much de- 
corticated in the only shell seen; left valve with a long, curved 
upper pseudocardinal formed no doubt by the union of two 
teeth, and a small ragged tooth below it and two remote, curved 
laterals, the upper very small; beak cavity enormous and pro- 
found, not compressed; dorsal scars at the base of the pseudo- 
cardinals; posterior scars shallow; anterior scars ragged; 
nacre whitish, pink-tinted. 
Length 77, height 64, diam. 55 mm. 
Usumacinta River, Guatemala. 
The National Museum possesses a single valve of this ro- 
bust species presented by Dr. von Ihering. I at first referred 
it to the Unio usumasinte with doubt, but I am now satisfied 
that it is not that, but an undescribed species. It is much more 
rudely sculptured than that species and has a totally different 
epidermis, the beaks are nearer the anterior end of the shell, 
and the outline below them is an ogee, while it is truncate 
above in usumasinte. Its beaks are turned farther forward 
and the enormous beak cavity is much deeper. On account of 
this immense and deep cavity I have called it Quadrula pro- 
funda. 
QUADRULA USUMASINTA (Crosse and Fischer). 
Shell subtriangular, inflated, very solid, cordiform with a 
high umbonal region greatly raised above the hinge; beaks 
turned upward and forward over a wide lunule; anterior end 
slopingly truncate above, rounded below; posterior end slop- 
ingly truncate; posterior ridge distinctly double, ending in a 
biangulation just at and above the base; beak sculpture con- 
sisting of rather fine, irregular, subnodulous ridges; this grad- 
ually passes into the strong, irregular, concentric sculpture 
covering the shell, these ridges are granular in front and fee- 
bly subnodulous behind; on the posterior slope there are radial, 
nodulous wrinkles and a few faint, radial folds on the front 
part of the shell; ligament long, brown; epidermis ashy or 
ashy-brown; hinge very strong; left valve with two large, con- 
