PLEUROBEMA 789 
curved up behind; posterior ridge high, angled, ending behind 
in a point near the base; dorsal slope obliquely truncated, 
meeting the dorsal line at an angle; epidermis greenish-brown ; 
left valve with two low, rough, rather solid pseudocardinals 
and two short, straight laterals; right valve with one pseudo- 
cardinal and one lateral, the latter inclined to be double ; mus- 
cle scars small, shallow ; beak cavities compressed ; nacre whit- 
ish, iridescent behind. 
Length 40, height 28, diam. 17 mm. 
Type locality, Roanoke River, Weldon; also Salem, North 
Carolina. 
Umo striatulus Lea, Pr. Acad. N. Sci. Phila., I, 1857, p. 86; 
ie Necad Ne Set. (Phila. V_.1862, p-.55; pl. 1, fig..202,; Obs., 
VIII, 1862, p. 59, pl. 1, fig. 202.—Sowerpy, Conch. Icon., 
XVI, 1868, pl. Lxxu, fig. 367——SIMPSON, Syn., 1900, p. 719. 
Margaron (Unio) striatulus La&a, Syn., 1870, p. 37. 
Conchologically this and a few other apparently related spe- 
cies seem closely allied to the Unio argenteus of Lea, and I am 
now inclined to place them in that assemblage notwithstanding 
the fact that they are found in the Atlantic drainage. The 
beak sculpture of these forms, so far as I can ascertain, is rath- 
er strong ridges which turn up sharply behind and this style of 
sculpture is more characteristic of Plewrobema than of Unio. 
Their peculiar distribution is no more remarkable than that of 
Lampsilis constricta, which is found in both the Atlantic and 
Tennessee areas. 
PLEUROBEMA FAVOSUM (I[,ea). 
Shell subrhomboid, subcompressed or convex, subsolid, in- 
equilateral; beaks rather full and high, their sculpture a few 
irregular corrugations; posterior ridge narrowly rounded, end- 
ing in a blunt point near the base of the shell; anterior end 
rounded ; base evenly curved; dorsal line nearly straight, meet- 
ing the obliquely truncated posterior slope with an angle; sur- 
face delicately, concentrically striate; epidermis yellowish- 
green or brownish, generally with a broad, ill-defined, broken 
ray in front of the posterior ridge ; pseudocardinals two in the 
