530 UNIO 
tle reflexed, smooth below, those of the left valve partly unit- 
ed; muscle scars smooth; nacre whitish to salmon. Animal 
the same as described for the section. 
Unto picroruM (Linnzeus ). 
Shell elongated, convex to subinflated, inequilateral, sub- 
solid; dorsal and ventral lines nearly parallel; anterior end 
rounded or subtruncate, usually slightly angular above; pos- 
terior ridge full and rounded, ending behind in a point about 
at the median line; the outline of the base is generally a little 
angulated at some distance in front of the posterior end; beaks 
full and elevated, their sculpture consisting of double-looped 
ridges, the anterior loop rounded, the posterior one angled, 
the ridges in a majority of cases more or less broken into nod- 
ules, which are often scattered; surface nearly smooth, show- 
ing only delicate growth lines; epidermis bright, greenish-yel- 
low, yellowish-green, straw-color, yellow or tawny, occasionally 
feebly rayed behind and in most cases showing the dark rest 
periods; left valve with two compressed pseudocardinals, the 
hinder sometimes partly double and extending forward below 
the anterior one, with two delicate, straight laterals, the lower 
the larger; right valve with two compressed pseudocardinals, 
the upper much smaller and one high, lamellar lateral; beak 
cavities moderately deep; nacre silvery-white, sometimes flesh- 
color or salmon, a little thicker in front; muscle scars nearly 
smooth, impressed in solid shells. 
Length 100, height 43, diam. 30 mm. 
Length 80, height 34, diam. 23 mm. 
Europe generally ; Siberia east to the Lena River and per- 
haps farther; south into Asia Minor?; Algiers? 
Mya pictorum Linnatus, Syst. Nature, toth ed., 1758, I, p. 
671. PENNANT, ‘Brit. Zool; -1 V7.2 ap). Ee li 
Da Cosra). Hist...Nat.. Brit., 1778; ps 228, (plex nese 
ScHROTER, Flussconch., 1779, p. 178, pl. 11, figs. 2, 4, 5.— 
Sturm, Deuts. Faun., VI, 1803, 2d ed., p. 19, pls. a, b, ¢— 
Woop, Gen. Conch., I, 1815, p. 104, pl. xrx, figs. 3, 4; Index 
Test..1825, 1p. 12) ply mm, fig. 26c; reve ed 1650, p. 05, pl. um; 
fig. 26.—? CuEnu, Bib. Conch., 1st ser., I, 1845, p. 1414, pl. 
114, pl. xivit, figs. 8, 9. 
