790 PLEUROBEMA 
left valve and one in the right; left valve with two laterals : 
right valve with a somewhat double one; beak cavities not 
deep; muscle scars small, shallow; nacre whitish, thinner and 
iridescent behind. 
Length 50, height 33, diam. 18 mm. 
Alabama River system. 
Type locality, Othcalooga Creek, Gordon Co., Ga. 
Umio favosus les, Proc. Ac. N. Sci. Phila., VIII, 1856, p. 262; 
jl. Ac.ON. Sci. Phila:; TV 1858) pe 58. pliavan, ties yom Oboe 
VI, p. 58, pl. vir, fig. 40-—SowkERBy, Conch. Icon., XVI, 
1868, pl. xc, fig. 488. 
Margaron (Unio) favosus Lea, Syn., 1870, p 38. 
Pleurobema favosa SIMPSON, Syn., 1900, p. 76T. 
The shell approaches that of several species, simulans, ar- 
genteum, amabile and patsaligense, etc. It is larger and light- 
er colored than simulans, smaller, brighter colored and more 
curved on the base than argenteum, larger, more compressed, 
and greener than amabile, thinner and more rounded below 
than pyriforme, more elongated than patsaligense and does 
not have fine rays. It must be confessed that many of the 
forms I have placed in this group are close and puzzling, that 
a good many specimens are found that cannot be referred with 
certainty to anything. The types of all these species are dis- 
tinct enough and I have not felt that the material I have seen 
would justify me in uniting them. The base is sometimes 
swollen just behind the middle. 
PLEUROBEMA LENTICULARE (Lea). 
Shell between subtriangular and subrhomboid, subcompress- 
ed, rather solid, somewhat inequilateral; beaks apparently not 
very full or high; posterior ridge rather low, slightly double, 
ending below the median line in a biangulation; anterior end 
faintly and obliquely truncate above, rounded below; base line 
lightly curved; outline of dorsal slope curved; epidermis close- 
ly, concentrically wrinkled, brownish, showing feeble rest 
marks; left valve with two triangular pseudocardinals and 
two curved laterals; right valve with three pseudocardinals, 
