UNIO 617 
A most variable species, which has close relationships with 
the complanatus group. The disk is often sculptured with 
subvertical furrows and it is occasionally subnodulous. Some 
of the compressed specimens approach U. roanokensis, but are 
rougher and have a more distinct posterior ridge. The type 
is a young shell. 
UNIO MONROENSIS Lea. 
Shell subrhomboid, convex or subinflated, subsolid, inequi- 
lateral; beaks rather full and elevated, their sculpture appar- 
ently a few corrugated, longitudinal ridges; posterior ridge 
well developed, angled, ending behind in a point near the base ; 
base line curved; post-dorsal area obliquely subtruncated ; an- 
terior end round; surface nearly smooth, the dorsal slope 
sometimes having a few wrinkles; epidermis reddish or olive- 
brown, darker behind; left valve with two small, ragged, sub- 
compressed pseudocardinals and two delicate, curved laterals ; 
right valve with one or two pseudocardinals, the upper, when 
present, always small, and one lateral; muscle scars rather 
shallow ; nacre brilliant, purplish or violet, iridescent behind. 
Length 70, height 43, diam. 25 mm. 
Florida. 
Type locality, Lake Monroe, Fla. 
Unio monroensis Lesa, Desc. of 12 sp. of Uniones, 1843, no 
pasination: “ir. Am. Phil. Soc. EX; 1845?; p. 270, pl. Xxt, 
fig. 8; Obs., IV, 1848, p. 37, pl. xu, fig. 8—Simpson, Pr. 
U2. Natoiiuss XV 21892,.p. Ate; pl. Li; fig. 1; Syn., 1900, 
p. 710. 
Margaron (Unio) monroensis Lea, Syn., 1852, p. 29; 1870, p. 
40. 
Lea has only a single specimen, the type, in his collection and 
it differs a little from anything else | have seen. The posterior 
ridge curves up in the middle while in other shells, which seem 
to be this, it curves down medially. There seems to be an 
almost absolute transition from this species to U. hartwrighti 
and U/. hinklevyi. 
