UNIO 
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UNIO DELESSERTI Bourguignat. 
Shell subrhomboid, rather short, inequilateral, subcompress- 
ed, apparently subsolid ; beaks elevated a little above the dorsal 
line but not full, their surface rugose; posterior ridge widely 
double, ending behind near the base of the shell in a wide 
biangulation ; surface densely, concentrically striated; epider- 
mis yellow, faintly rayed with brown; pseudocardinals sub- 
compressed, ragged; laterals nearly straight, lamellar; nacre 
reddish. 
Length 49, height 32, diam. 17 mm. 
Syria. 
Umio delessertt Bourcuicnat,, Voy. Mer. Mort., 1852, p. 77; 
Cat. Rais. Moll., 1853, p. 77, pl. 1, figs. 7-9—SImMPsoN, 
Syn., 1900, p. 692.—KoseExT, Icon., new ed., XIX, 1912, p. 
33, pl. DXXvII, fig. 2728. 
Margaron (Unio) delesserti Lea, Syn., 1870, p. 46. 
Extremely close to U. duriew apparently and probably only 
a variety of it. It is higher in proportion to the length than 
any specimens | have seen of that shell; it is more widely and 
distinctly biangulate behind and the nacre is reddish, a tint 
1 have never seen in that species. . 
UNIO SEMIRUGATUS Lamarck. 
Shell short, subrhomboid, convex to subintlated, somewhat 
inequilateral, solid; beaks full and high, their sculpture con- 
sisting of broken ridges often arranged in checker board pat- 
tern; sometimes they are slightly chevron-shaped or zigzag- 
ged; posterior ridge faint, rounded or rarely biangulate; sur- 
face usually rudely. and unevenly sculptured by the growth 
lines; epidermis ashy, pale olive or yellowish-green and often 
rayed in the young, becoming dark brown in the old shells; 
left valve with two pseudocardinals, the anterior compressed, 
often joining the more solid posterior one, and two curved 
laterals; right valve with one pseudocardinal, with vestiges 
of one in front, and another behind and one lateral; beak cav- 
ities rather deep ; muscle scars impressed ; nacre whitish, some- 
