872 QUADRULA 
secondary lateral in the right valve; cavity of the beaks gen- 
erally deep and compressed ; muscle scars small, deep. 
Animal with the marsupium occupying the whole of all four 
branchiz, inner gills generally free from the abdominal sac, 
much wider than the outer in front; outer nearly or quite 
equaling them in width behind; anal opening distinctly crenu- 
late or papillose. 
QUADRULA RUBIGINOSA (Lea). 
Shell rhomboid, compressed to slightly inflated, swbsolid to 
solid, equilateral or inequilateral; beaks high, generally full, 
turned forward over a Junule, their sculpture a few corruga- 
tions that curve up strongly behind; anterior end rounded, of- 
ten slopingly truncate above; base line sometimes slightly 
curved, usually straight or feebly sinused in front of the pos- 
terior ridge; dorsal slope angled in the middle, obliquely trun- 
cate below; posterior ridge high, subangular or narrowly 
rounded, ending in a point at the base of the shell; surface 
with more or less irregular, concentric sculpture; epidermis 
brown or greenish-brown, sometimes feebly rayed, cloth-like 
when fresh; pseudocardinals triangular, more or less ragged ; 
lateral in the right valve single or double; beak cavities rather 
deep; muscle scars impressed; nacre bluish-white to salmon- 
tinted, thinner and iridescent behind. 
Length 110, height 80, diam. 45 mm. 
Length 71, height 52, diam. 29 mm. 
Length 68, height 51, diam. 23 mm. 
Length 8o, height 68, diam. 42 mm. 
Entire Mississippi drainage; eastern Texas; St. Lawrence 
River system; Nelson River and its tributaries. 
Type locality, Ohio. 
Unio rubiginosus Lea, Tr. Am. Phil. Soc., III, 1829, p. 427, 
pl. vir, fig. 10; Obs., I, 1834, p. 41, pl. vim, fig. 10.—HAaAnN- 
LEY, Biv. Shells, 1843, p. 185, pl. xx1, fig. 43.—CHENU, IIl. 
Conch., 1858, pl. xt, figs. 4, 4a, 4b.—REEvE, Conch. Icon., 
XVI, 1865, pl. xxvu, fig. 136—Watton, Moll. Monroe Co., 
1892, p. 16, pl. vit, fig. I. 
