PLEUROBEMA Heyl 
Unio validus Ia, Pr. Ac. N. Sci. Phila., I, 1871, p. 189; Jl. Ac. 
N. Sci. Phila., VIII, 1874, p. 6, pl. 1, fig. 2; Obs., XIII, 1874, 
pL kO; pli, fig. -2. 
Pleurobema valida Simvson, Syn., 1900, p. 749. 
This shell is more distinctly triangular than its allies; the 
rays are rather narrow on the only examples I have seen, and 
are scarcely broken. 
PLEUROBEMA TUMESCENS (Lea). 
Shell nearly triangular, inflated, solid, inequilateral; beaks 
long, very high and full; lunule large; anterior end decidedly, 
obliquely truncated above, rounded below; base line nearly 
straight ; outline of the dorsal slope slightly curved; posterior 
ridge well developed, rounded, the shell being only a little 
fuller in front of it; surface with uneven growth lines; epider- 
mis greenish-yellow to tawny, faintly rayed; pseudocardinals 
irregular, two in the left valve and three in the right; laterals 
curved, two in the left valve and a double in the right ; beak 
cavities shallow; muscle scars small, moderately deep; nacre 
white or yellowish. 
Length 43, height 40, diam. 27 mm. 
Tennessee. The localities, Alexandria, Louisiana, of Lea, 
of the type, and Ouachita River, given by Call, are open to 
doubt. 
Unio tumescens La, Pr. Am. Phil. Soc.. IV, 1845, p. 164; Tr. 
Am: Phil: Soc, Xx, 1848, p. 71, pl: m1 fie.-7 ; Obs.; 1V, 1848, 
(Fe At my 8) un cr a Keane 
Margaron (Unic) tumescens Lea, Syn., 1852, p. 25; 1870, p. 
38. 
Pleurobema tumescens SIMPSON, Syn., 1900, p. 750. 
Umo radiosus lea, Pr. Ac N. Ser. Phila. 1, 1871, p. 192; Jl. 
Ac, Necocterhila,, Villy s137421p) <3; pli 1m, figs -93-/Obs., 
ML 18745 /p. a7 plyan, figso. 
Close to dolabelloides but more strictly triangular and small- 
er. The beaks are not quite so high nor so much curved for- 
ward as in that species. I cannot see that radiosus differs in 
any character from tumescens. 
