PLEUROBEMA gpa 
double one in the right; muscle scars small, impressed; beak 
cavities shallow ; nacre white, thinner and iridescent behind. 
Length 35, height 28, diam. 20 mm. 
Length 44, height 35, diam. 29 mm. 
Coosa River system. 
Type locality, Etowah River, Ga. 
Unio irrasus Lua, Pr. Ac. N. Sci. Phila., V, 1861, p. 38; Jl. 
Ac N= sect. Phila. V_1862,-p. or, pl. x11, fig: 239% Obs., 
VIII, 1862, p. 95, pl. x1u, fig. 230. 
Margaron (Unio) irrasus Lea, Syn., 1870, p. 38. 
Pleurobema irrasa SIMPSON, Syn., 1GO0, p. 756. 
Close to troschelianum, but it is not so elongated, it is more 
nearly triangular and the beaks are nearer the center of the 
shell. It is quite likely that the two forms may run together. 
PLEUROBEMA ALTUM (Conrad). 
Shell suborbicular or somewhat subtriangular, inflated, solid, 
subequilateral; beaks high, full and rounded; anterior end 
nearly evenly rounded, sometimes very faintly subtruncate 
above ; base line much rounded; outline of dorsal slope slightly 
curved, raised into a slight angle behind the ligament ; poste- 
rior ridge strong, narrowly rounded, generally narrowly double 
below, ending below the median line in a narrow biangulation ; 
surface with irregular growth lines; epidermis dirty tawny or 
tawny-brown, sometimes having a few faint, squarish, green 
spots; pseudocardinals subtriangular, two in the left valve, 
one to three in the right; laterals very short and heavy; two 
in the left valve and a double one in the right; beak cavities 
shallow; muscle scars small, deep; nacre white, thinner and 
iridescent behind. 
Length 35, height 33, diam. 21 mm. 
Alabama River system. 
Type locality, Tennessee. ? 
Unio altus Conran, Jl. Ac. N. Sci. Phila., II, 1854, p. 298, pl. 
XXVU, fig. 5. 
Margaron (Unio) altus Lea, Syn., 1870, p. 42. 
Pleurobema alta Stmpson, Syn., 1900, p. 756. 
