552 UNIO 
I am very doubtful whether this is more than a mere varia- 
tion of U. pietri. It is a little more nearly oval or elliptical 
and is nearly or quite destitute of the upper anterior angle. 
UNIo DELIcatus Lea. 
Shell almost evenly elliptical, convex, inequilateral, sub- 
solid, with rather high but not full beaks, their sculpture con- 
sisting of irregular, nodulous ridges, which have a tendency 
to be doubly looped, the sculpture extending well out on to 
the disk in the form of uneven nodules; posterior ridge low, 
rounded, ending at the median line in a blunt point; dorsal 
line nearly straight ; anterior end a little narrowed and round- 
ed; surface with delicate, uneven growth lines; epidermis pale 
greenish-yellow, with one or two faint rays on the post-dorsal 
slope: teeth delicate, the pseudocardinals compressed; nacre 
whitish. 
Length 27, height 16, diam. 10 mm. 
Orontes River. Syria. 
Umo delicatus Lea, Pr. Acad. N. Sci. Phila., VII, 1863, p. 189. 
—Jl. Acad. N. Sci. Phila., VI, 1866, p. 58, pl. x1x, fig. 56.— 
Obs. XI, 1867, p. 62, pl. x1x, fig. 56—SimMpson, Syn., 1900, 
p. 690.—Koset, Icon., new ed., XVIIT, 1912, p. 45, pl. pu, 
fig. 2657. 
Margaron (Unio) delicatus LEeA, Syn., 1870, p. 42. 
This is no doubt a young shell and really ought not to have 
been described. It is quite likely that U. ellipsoideus is the 
adult of it. Its only decided character is the beak sculpture, 
which extends out on to the disk in the form of scattered, ir- 
regular nodules or granules. 
Group of Unio littoralis. 
Shell rather solid, subinflated, rounded rhomboid, with a 
faint posterior ridge, usually slightly biangulate behind, and 
often becoming arcuate when old; beaks prominent and full; 
beak sculpture consisting of numerous rather fine, subparallel 
ridges or corrugations, which are sometimes a good deal brok- 
