898 QUADRULA 
wrinkled ; pseudocardinals subradial, usually curved, split up 
and torn; lateral of right valve disposed to be double; muscle 
scars deep; beak cavities very deep, compressed; nacre white, 
thinner and iridescent behind. 
Length 110, height 92, diam. 60 mm. 
Length 102, height 75, diam. 55 mm. 
Length go, height 74, diam. 53 mm. 
Mississippi drainage generally, except its western portion; 
Alabama and Tombigbee Rivers; northeast Texas? 
Type locality, Ohio River. 
Unio ebenus Lea, Tr. Am. Phil. Soc., IV, 1831, p. 84, pl. 1x, 
fig. 14; Obs., I, 1834, p. 94, pl. 1x, fig. 14—Han ey, Biv. 
Shells, 1843, p. 202, pl. xx, fig. 47——CuHeENu, III. Conch., 
1858, pl. xv, figs. 7, 7a, 7b——SoweERBy, Conch. Icon., XVI, 
1868, pl. Lxvi, fig. 334. 
Margarita (Unio) ebenus Lua, Syn., 1836, p. 34; 1838, p. 23. 
Margaron (Unio) ebenus Lea, Syn., 1852, p. 35; 1870, p. 56. 
Ouadrula ebents SIMPSON, Syn., 1900, p. 793. 
Fusconaja ebena OrtMANN, Ann. Car. Mus., VIII, 1912, p. 
245. ne ais 
Unio obovalis Say, Am. Conch., VI, 1834. 
Unio obliquus Conran, Monog., [X, 1837, p. 77, pl. xia, fig. 
2.—Kuster, Conch. Cab. Unio, 1861, p. 215, pl. Lxx1, fig. 4. 
Unio mytiloides Swatnson, Treatise on Mal., 1840, p. 270, 
figs. 52, 53. 
An abundant, widespread and variable form. It is the “‘nig- 
gerhead” of button manufacturers of the Mississippi River 
and the most valuable and important species used by them. 
It has exceedingly full, high beaks, which are usually placed 
at the extreme anterior end of the shell. The lunule is gener- 
ally placed farther back than in allied species; in fact, the 
beaks often project in front of it. There is sometimes a faint 
secondary lunule. The young are often light ashy-brown on 
the beaks with a pale or whitish area on the dorsal slope, very 
different from those of any related forms. 
