QUADRULA 823 
epidermis dark brown or blackish; pseudocardinals somewhat 
split up radially ; laterals lamellar; muscle scars large, shal- 
low, the anterior partly filled with roughened nacre; nacre 
white. 
Length 125, height 92, diam. 46 mm. 
Rio Usumacinta, Guatemala. 
Unio digitatus Moree, Test. Noviss., Pt. 2, 1851, p. 24.— 
FiscHrr and Crossr, Miss. Sci., II, 1894, p. 563, pl. Lx, fig. 1. 
Quadrula digitata SIMPSON, Syn., 1900, p. 770. 
The prominent and distinguishing characters are the radiat- 
ing ribs, about 15 in number that start from behind the beak 
and along to a point lower down the disk and extend back- 
ward and outward to the extreme edge of the shell from the 
middle of the ligament to the base, and the small, regularly 
arranged pustules on the anterior end. 
QUADRULA TRIUMPHANS (B. H. Wright). 
Shell short, irregularly obovate, scarcely subinflated, inequi- 
lateral, solid: beaks low and compressed; anterior end nar- 
rowed and rounded; base line lightly curved; dorsal outline 
nearly straight, elevated into a wing; posterior end somewhat 
obliquely truncated above, widely rounded below ; surface cov- 
ered with concentric growth marks and narrowly spaced rest 
marks, having a series of folds, which radiate backward and 
outward from below the region of the beaks, these folds are 
strongest below and aré somewhat corrugated, broken and 
divaricate ; along the anterior end and anterior base there are 
numerous uneven tubercles; epidermis blackish; pseudocardi- 
nals rather small, radial and radially striate; laterals granu- 
late ; beak cavities deep and compressed; anterior scars small, 
slightly roughened: nacre whitish or flesh-color, thinner, pur- 
plish and iridescent behind. 
Length 105, height 94, diam. 40 mm. 
Type locality, Coosa River, St. Clair County, Alabama. 
Unio triumphans B. H. Wricut, Naut., XI, 1898, p. ror. 
Ouadrula triumphans Simpson, Pr. Ac. N. Sci. Phila., 1goo, 
p. 83, pl. 11, fig. 3; Syn., 1900, p. 770. 
