P1,EUROBEMA 741 
shining ; pseudocardinals low, irregular, rough, two in the left 
valve and three in the right; laterals curved, left valve with 
two, right valve with a double one; beak cavities shallow, 
muscle scars small, deep; nacre white. 
Length 30, height 32, diam. 19 mm. 
Length 38, height 40, diam. 26 mm. 
Type locality, Scioto River, near Chillicothe, Ohio. 
Unio bournianus Lea, Pr. Am. Phil. Sci., I, 1840, p. 288; Tr. 
Avex Phils soc. IV LEL Mr S42. p. 213) pl xv, he: 23: ‘Obs., IT, 
p- 51, pl. xv, fig. 28.—CHENU, Ill. Conch., 1858, pl. xxvii, 
figs. 2, 2a, 2b. 
Margaron (Unio) bournianus Lea, Syn., 1852, p. 25; 1870, 
P. 30. 
Pleurobema bournianus SIMPSON, Syn., 1900, p. 747. 
Lea has three shells, to which he gives this name. The 
larger one is considerably deformed, and the medium one, the 
type, is probably not exactly normal. I am doubtful whether 
the third, a young shell, is the same as the others. The species 
is close to edgarianum and may possibly be merely a slight 
malformation of that. It is higher than long and the beaks. 
are more pointed than they are in that species. 
PLEUROBEMA EDGARIANUM (Lea). 
Shell subtriangular, subinflated to inflated, solid, inequilat- 
eral: beaks full and high, turned forward a little over a lunule ; 
their sculpture a few strong, broken, subnodulous ridges; an- 
terior end obliquely truncated above, rounded below ; posterior 
end curved from the beaks to the base, often subangular just 
behind the ligament; base line nearly straight behind, curved 
up in front; posterior ridge well developed, curved so that it 
runs nearly parallel with the posterior outline, but placed some 
distance in front of it, narrowly rounded or angular, some- 
times slightly double below, ending in a point or biangulation 
at the base line: in front of the middle there is a wide radial 
swelling and here the diameter of the shell is greatest ; surface 
with uneven growth lines; epidermis greenish-yellow, yellow- 
green or brownish, in young shells generally having wide and 
