QUADRULA 833 
wide lunule, their sculpture a few irregular, strong ridges that 
are nodulous on the posterior ridge; posterior ridge full, 
rounded; above it there is usually a wide, radial impression 
that sometimes ends in a slight sinus behind; anterior end 
rounded, subangular above; posterior end squarely or oblique- 
ly truncate; sometimes there is a point behind below the me- 
dian line; surface with irregular, concentric sculpture, having 
a row of knobs extending along the posterior ridge and often 
more or less covered with lachrymous nodules and plications ; 
epidermis straw-color, tawny, yellowish-green or greenish-yel- 
low, generally overlaid with a pattern of triangular, green 
blotches, these are sometimes developed into radial stripes as 
if they had been painted on and had drizzled down; sometimes 
the green blotches are so close that they are only separated by 
narrow, greenish-yellow, zigzag lines, the whole smooth and 
somewhat shining; pseudocardinals radially split up; laterals 
long and straight ; anterior scars impresed; beak cavities deep, 
compressed; nacre silvery white, rarely purplish, iridescent 
and much thinner behind. 
Length 114, height 50, diam. 46 mm. 
Entire Ohio, Cumberland, and Tennessee river systems; 
west to Nebraska (Aughey, doubtful) ; south to Arkansas and 
Indian Territory. 
Type locality, Wabash River. 
Umio cylindricus Say, Nich. Encyc., I, 1817, pl. 1v, fig. 3.— 
HitpretH, Am. Jl. Sci, XIV, 1828, p. 283, figs. 13, 13b.— 
HANLEY, Biv. Shells, 1843, p. 182, pl. xx, fig. 31—KusTEr, 
Conch. Cab. Unio, 1861, p. 194, pl. Lx, figs. I, 2—SOwER- 
By, Conch. Icon., XVI, 1867, pl. Lx, fig. 300—Catu, Tr. 
ead. Set, St. ous, Vil, 895, p:-15,-pl. x11. 
Margarita (Unio) cylindricus Lea, Syn., 1836, p. 17; 1838, p. 
10. 
Margaron (Unio) cylindricus Lea, Syn., 1852, p. 23; 1870, p. 
35: 
Orthonymus cylindricus Acassiz, Arch. fiir. Naturg., I, 1852. 
p. 48. 
Mya cylindrica Eaton, Zool. Text-Book, 1826, p. 210. 
