$38 QUADRULA 
Unio mtermedius CONRAD, Monog., VII, 1836, p. 63, pl. xxxv, 
fig. 2—Han.ey, Biv. Shells, 1856, p. 381, pl. xx, fig. 28.— 
Kuster, Conch. Cab. Unio, 1861, p. 213, pl. Lxx, fig. 6.— 
REEVE, Conch. Icon., XVI, 1864, pl. x11, fig. 48. 
Margaron (Unio) intermedius Lea, Syn., 1852, p. 22; 1870, 
D. 33: 
Quadrula intermedia SIMPSON, Syn., 1900, p. 775. 
Unio kleinianus Kusver, Conch. Cab. Unio, 1861, p. 191, pl. 
EX, ea As 
More compressed and lenticular, more nearly round or short 
elliptical than tuberosa, to which it sometimes closely approach- 
es. The posterior radial depression is deeper and more sin- 
uate behind than in any member of the group and the posterior 
ridge is less elevated or produced below. 
QUADRULA STAPES (Lea). 
Shell irregularly quadrate, subinflated to inflated, solid, equi- 
lateral; beaks high but not very full; posterior ridge high, 
narrowly rounded or subangular, behind it there is a radial 
depression and the posterior end of the shell is decidedly trun- 
cated: anterior end rounded; base rounded, straight behind, 
sometimes slightly incurved in front of the posterior ridge; . 
surface covered with warts or lachrymose tubercles; these 
are sometimes triangular or formed into broken, zigzag 
ridges; epidermis yellowish-green in the young shells with 
fine, zigzag or triangular green markings; old shells usually 
brown; pseudocardinals radial, ragged; laterals short, that 
of the right valve double; beak cavities deep, compressed ; 
muscle scars small, impressed; nacre silvery white, thinner and 
iridescent behind. 
Length 60, height 53, diam. 27 mm. 
Length 49, height 44, diam. 36 mm. 
Alabama and Tombigbee rivers. 
Type locality, Alabama river. 
Umo stapes Lea, Tr. Am: Phil. Soc. 1V, 1831, p- 77, pl. vil, 
fig. 8; Obs., I, 1834, p. 87, pl. vu, fig. 8—Conrap, Monog., 
VII, 1836, p. 62, pl. xxxv, fig. 1—HANtEy, Biv. Shells, 
1843, p. 179, pl. xxi, fig. 38.—CueEnu, Ill. Conch., 1858, pl. 
XV, figs. 5, 5a, 5b; Manual, 1859, II, p. 142, fig. 997.— 
Reeve, Conch. Icon., XVI, 1864, pl. x11, fig. 52. 
