PLEUROBEMA 749 
terior ridge well defined, narrowly rounded, curved, it is not 
so high as the wide radial swelling near the anterior end; 
between the two the surface is flattened ; surface with irregular 
growth lines; epidermis greenish-yellow to tawny, usually 
marked with narrow and wide, broken, green rays; pseudo- 
cardinals irregular, ragged, left valve with two, right valve 
with three, the lateral ones small; laterals two in the left 
valve and a double one in the right ; beak cavities shallow, com- 
pressed; muscle scars deep, small; nacre bluish to yellowish- 
white. 
Length 38, height 34, diam. 22 mm. 
Length 43, height 37, diam. 24 mm. 
Tennessee River system. 
Type locality, Tuscumbia, Ala.; Holston River, Tenn. 
Unio tuscumbiensis Lea, Pr. Ac. N. Sci. Phila., I, 1871, p. 191; 
(inc. No Sci, Pinta VILL 13874, p, 11, pli, Ag.7; Obs., 
Pee Logs. 5. Pl. Ao. 7 
Umio flavidus’ Lea, Pr. Ac. N. Sci. Phila., II, 1872, p. 156; J). 
Dew apcmrnia Vill 1a74, p. 28, pl 1x, fie. 2s5;--Obs., 
Mel aS74.-p. 32> pl. 1X, fig..25, 
Pleurobema appressa (part), SIMPSON, Syn., 1900, p. 749. 
Although there are specimens, which may be about as easily 
referred to P. appressum as to this, it may be best to separate 
the two. Generally this form seems to be smaller than ap- 
pressum, a little more inequilateral, and a little more inflated. 
Lea's Unio flavidus seems to me to be absolutely identical with 
his tuscumbiensis. 
PLEUROBEMA TESSERULA (Lea). 
Shell small, much inflated, subrhomboid, solid, inequilateral ; 
beaks high, full, but not much elongated, their sculpture ap- 
parently a few coarse ridges, which curve up behind; lunule 
small; anterior end narrowly rounded and gaping; base line 
nearly straight; dorsal line behind the beaks straight, meeting 
the oblique truncation of the dorsal slope at an angle ; posterior 
ridge full, narrowly rounded, ending behind in a rounded point 
at the base of the shell; surface finely but unevenly, concentri- 
cally striate; epidermis yellowish-green, marked with a few 
