608 UNIO 
Var. incrassatus Lea. 
Shell smaller, more rhomboid or quadrate than the type, 
wrinkled behind the posterior ridge and sometimes having 
subvertical corrugations on the disks. It is rather smoother 
than typical crassidens. 
iength 56, height 36, diam. 23 mm. 
Coosa River system; Chattahoochee and rivers of north 
Florida; east to Savannah ? 
Type locality, Chattahoochee River, Columbus, Ga. 
Unio mcrassatus Lea, Pr. Am. Phil. Soc., I, 1840,.p. 286; Tr. 
Am. Phil. Soc; Vill, 1840; pe2i7, pl Xvi, tessa Oss 
ITT, 1842, p. 55, pl. xvi, fig. 34.—Cuenu, Ill. Conch., 1858, 
pl. xxx, figs. 5, 5a, 5).—Kuster, Conch. Cab. Unio, 1861, 
p. 192, pl. Lx, fig. 5—Rerve, Conch. Icon., XVI, 1865, pl. 
XXVI, fig. 127,—SIMPSON, Syn., 1900, p. 707: 
Margaron (Unio) incrassatus Lea, Syn., 1852, p. 24; 1870, p. 
37: 
Usually considered as a valid species, but recent careful study 
and comparison of a large series of material has inclined me 
to place it as a variety under crassidens. A considerable 
number of intermediate specimens from the Tennessee and 
Coosa rivers seem to connect the two completely. 
Unio poLtyMorpuus B. H. Wright. 
Shell solid, convex to subinflated, generally more or less 
rhomboid, inequilateral ; beaks rather full, moderately elevated, 
their sculpture not observed; posterior ridge high and sharp, 
usually somewhat double below, ending in a point or biangula- 
tion at or near the base line; base line straight or slightly 
curved; rarely incurved in old shells; surface with irregular 
growth lines, wrinkled on the dorsal slope; epidermis thick, 
bronzy-green and rayed in the young, reddish-brown to black- 
ish in adult shells; left valve with two stout, ragged pseudo- 
cardinals and two laterals; right valve with one pseudocardinal 
and a small tooth above it, with one, often somewhat double, 
