560 UNIO 
surface with moderate growth lines, covered with a thick, 
rather rough, dark brown or blackish, epidermis, which is 
inclined to peel off; left valve with two small stumpy, nearly 
smooth pseudocardinals and two low, club-shaped laterals, the 
upper small; right valve with one stumpy pseudocardinal and 
a vestigial one behind it, with a single club-shaped lateral ; 
hinge plate rather wide; beak cavities deep, compressed ; mus- 
cle scars deep, the anterior roughened; nacre rich purple, 
thickened in front. 
Length 96, height 56, diam. 33 mm. 
Length 70, height 41, diam, 24 mm. 
Syria. 
Unio homsensis Les, Proc. Nat. Sei. Phila., VIII, 1864, p. 285 ; 
Jl. Acad. Nat. ‘Sei. Phila, VI, 1868, p: 240, ‘pl. xxix; fie: 
63; Obs. XII, 18609, p. 9, pl. xxix, fig. 63—SIMPSON, Syn., 
1900, p. 693.—Kosxrr,1, Icon., new ed., XVIII, 1912, p. 53, 
pl. pvi, fig. 2669. ~ 
Margaron (Unio) homsensis Lava, Syn., 1870, p. 31. 
Two opposed valves of this species are all the material I 
have seen. In the smaller of these the posterior slope is slightly 
corrugated. It is more elongated than U. littoralis, and the 
nacre is a rich purple. 
Unio PSEUDONYMUS Simpson. 
Shell irregularly subrhomboid, much inflated, solid, inequi- 
lateral; beaks high and full, with peculiar tuberculated sculp- 
ture; posterior ridge not well developed, rounded; posterior 
end subtruncated ; anterior end cut away slightly below; dorsal 
and basal lines rounded; surface apparently having rather 
strong concentric sculpture, greenish-yellow, darker behind 
with a few narrow rays on the posterior half of the shell; 
ligament large; pseudocardinals solid, crenate; laterals elon- 
gated; muscular impressions distinct; nacre white, iridescent. 
Length 75, height 42, diam. 34 mm. 
Euphrates and Tigris rivers. 
Unio hueti Korner, Icon., new ser., II, 1886, p. 22, pl. x1, fig. 
22 
Unio pseudonymus Stmpson, Syn., 1900, p. 694. 
