PLEUROBEMA 737 
? Unio patulus Lea, Tr. Am. Phil. Soc., III, 1829, p. 44. pl. 
x11, fig. 20; Obs., I, 1834, p. 55, pl. xu, fig. 20.—Conrap, 
Monog., X, 1838, p. 92, pl. L, fig. 2—HANLeEy, Biv. shells, 
1843, p. 187, pl. xxu, fig. 27—CueENU, Ill. Conch., 1858, pl. 
XVI, figs. 6, 6a, 6b.—Kuster, Conch. Cab. Unio, 1861, p. 
250, pl. LXXxXvIl, fig. 5. 
Margarita (Unio) patulus Lea, Syn., 1836, p. 22; 1838, p. 18. 
Margaron (Unio) patulus Lea, Syn., 1852, p. 26; 1870, p. 40. 
Unio cuneatus Say, Am. Conch., VI, 1834. 
One of the most striking of North American Uniones. The 
species is excessively variable in form and it is remarkable 
that these variations have not oftener received specific names 
at the hands of students. In some cases the very high beaks 
project considerably ahead of any other part of the shell, the 
anterior end below them being cut away with a strong, straight, 
oblique truncation. At other times the beaks do not reach 
quite to the anterior end, this end may be rounded or squarely 
truncated; the truncation even slopes backward at the top i 
some cases.. Specimens so shaped approach the form I have 
taken for Unio maculatus of Conrad. There is a hitch of some 
kind about Lea’s Unio patulus, which I cannot untangle. Dr. 
Lea states that it came from T. G. Lea, from Ohio and he fig- 
ures a shell that is shaped almost exactly like that of his U. 
lesleyi, which is from Kentucky and Tennessee. J have never 
seen stich a shell from Ohio and I am inclined to think that the 
figure was made from a rather brightly rayed Jesleyi. All Lea’s 
specimens marked patulus are quite different from the figure 
and are evidently clava. 
PLEUROBEMA MACULATUM (Conrad). 
Shell subtrianguiar, compressed to subinflated, rather solid ; 
beaks prominent and inflated, their sculpture apparently a few, 
not very strong, irregular ridges; lunule small; anterior end 
nearly evenly rounded, projecting a little in front of the beaks ; 
base line nearly straight ; posterior and post-dorsal outline sub- 
truncated, slightly curved, raised almost into a low angle near 
the hinder end of the ligament: posterior ridge well developed, 
suhangular above, narrowly rounded below, ending behind near 
