600 UNIO 
Type locality, Branch of South Fork of the Cumberland 
River, Armathwaite, Fentress Co., Tennessee; also Mammoth 
Cave, Green County, Kentucky. 
Unio gibbesus var. armathwaitensis B. H. Wricut, Naut., XI. 
1898, p. 123.—Si1MPSON, Syn., 1900, p. 704. 
Var. delicatus Simpson. 
Shell subsolid or rather thin, subcompressed or compressed, 
subrhomboid or almost evenly elliptical, never arcuate. 
Length 98, height 36, diam. 18 mm. 
Greenway, Clay County, Arkansas; widely distributed in 
the Mississippi valley and into Michigan. 
Unio gibbosus var. delicatus SIMPSON, Syn., 1900, p. 704. 
Much more delicate than the type, rather thin, compressed, : 
not arcuate. 
UNIO STONENSIS Lea. 
Shell oblong, irregularly elliptical or subrhomboid, solid, 
compressed or subcompressed, inequilateral; beaks scarcely 
elevated above the dorsal line, compressed, somewhat pointed 
and turned forward over a narrow lunule, their sculpture 
consisting of moderately to quite coarse, subcorrugated ridges 
that follow the growth lines; posterior ridge well marked, 
somewhat double, running near the dorsal line and ending 
behind in a feeble biangulation below the median line; ante- 
rior end rounded ; dorsal line curved; base line slightly curved 
or nearly straight; surface with rude, uneven growth lines; 
epidermis tawny or tawny-brown; left valve with two stumpy, 
striated pseudocardinals the anterior small and two short, re- 
mote, slightly curved laterals; right valve with one pseudo- 
cardinal, the hinge being radially striate before and behind it 
and showing vestiges of teeth, with one strong, granulated 
lateral; beak cavities very shallow; dorsal scars close to the 
hinge plate; muscle scars deep and smooth; nacre white, some- 
times salmon-tinted in the center, a little thicker in front, 
obliquely furrowed. 
Length 84, height 47, diam. 22 mm. 
