QUADRULA 861 
QUADRULA AURFA (Lea). 
Shell subrhomboid, subcompressed to convex, inequilateral, 
subsolid; beaks slightly elevated, rather compressed, their 
sculpture a few coarse, irregular ridges; posterior ridge round- 
ed; anterior end rounded; base straight or lightly curved ; pos- 
terior end obliquely, rarely squarely, truncate; surface nearly 
smooth; there are occasionally faint plications on the dorsal 
slope and a few feeble nodules on the disk; epidermis yellow- 
ish-tawny or brownish, rarely greenish or having slight green- 
ish markings, scarcely shining; pseudocardinals radial, some- 
what split up; lateral of the right valve single or somewhat 
double; beak cavities moderately deep, compressed; muscle 
scars not deep; nacre whitish, often purple-tinted, iridescent 
behind. 
Length 62, height 46, diam. 21 mm. 
Length 56, height 39. diam. 23 mm. 
Length 50, height 34, diam. 22 mm. 
Type locality, Texas. 
Unio aureus Lea, Pr. Ac. N. Sci. Phila., ITI, 1859, p. 112; Jl. 
Ac. N. Sci. Phila., V, 1862, p. 195, pl. xxvi, fig. 264; Obs., 
IX. 1863, p. 17, pl. xxvr, fig. 264—Sowersy, Conch. Icon., 
XVI, 1868, pl. Lxxxm1, fig. 438. 
Margaron (Unio) aureus Lea, Syn., 1870, p. 37. 
Quadrula aurea StmPsoN, Syn., 1900, p. 783. 
Unio bolli Catt, Am. Naturalist, XV, 1881, p. 390. 
This species is usually more elongated and more rhomboid 
than petrina, less solid and inflated, smoother, and not so 
brightly painted. Its beak cavities are generally shallower, 
and the beaks are more compressed. Yet there are intermedi- 
ates that are hard to place. 
QUADRULA ARCHER: Frierson. 
“Shell small, thin, lenticular, somewhat quadrate, smooth. 
Anterior margin rounded, basal margin slightly curved, dor- 
sal margin somewhat bent midway, posterior margin rounded 
or bluntly pointed. umbones low and flattened. Sides com- 
pressed, raised slightly at the posterior angle, which is nearly 
