TRIBE OSTRACEA. 311 
when mature, oval when young, depressed, except near the umbones, 
pale brown, with russet brown radiating lines that are chiefly dis- 
posed in pairs and are obsolete on the hinder side; surface in fresh 
examples somewhat roughened by crowded concentric lamellar 
wrinkles, devoid of radiating ones. 4. Red Sea; Australia. 
V. Hians. (Gualt. t. 90, f. H.)— Mya Vutsgtia, young, Ch. 
F.10.—V. H., Lam. 2.—(? Sav. Egy. t.14, f. 3.) Oblong, sub- 
arcuated, tumid, brown with paler radiating lines: gaping on both 
sides, especially the hinder one. 23. Indian Ocean. 
V. Rugosa. Lam. 3.—Del. t. 18, f. 3. Oblong, subarcuated, 
flattened, tawny-brown, not radiated, decussated by longitudinal and 
transverse wrinkles: anterior margin strongly arcuated, scarcely, if 
at all, gaping. 2. 
V. Sponerarum. Lam. 4.—? Mya Vutsetya Minor, Ch. f. 8, 9, 
copied H. t. 178, f. 5. Oblong, straight, somewhat attenuated near 
the beaks, with concentric wrinkles, the longitudinal ones obsolete: 
internal nacre with a violet tinge. 1%. Indian Ocean. The epi- 
dermis thin, greyish and longitudinally wrinkled. 
V. Myrinina. Lam. 5. Large, elongated, white, but with the 
vestiges of darker radiating lines, with merely the wrinkles of 
increase; valves convex, athehusted near the hooked beaks, flattened 
and dilated at the opposite extremity. 5. Perchance a bleached 
Lineunata. 
V. Ovata. Lam.6. Oval-elliptic, rather depressed, somewhat 
violet, never rayed; with merely concentric lines of increase: nacre 
pearly. 14. Australia. 
V. Norratim. Conr. Jour. Ac. N.S. Phil. 7, p. 257, t. 20, f. 10. 
Very irregular, with concentric lamellar strive near the beaks: cavity 
of the interior deeply concave towards the hinge, bounded at the 
other extremity by a concentric ridge, the rest of the inner surface 
obliquely divided lengthwise by an obtuse rib. 1...4. Priendly 
Isles. Possibly a distorted specimen. 
PLACUNA. 
Shell free, subequivalve, irregular, very flat ; hinge consisting, in one 
valve, of two short longitudinal convergent ribs, in the form of the 
letter V placed upside down, which fit into two corresponding cartilage- 
grooves in the opposite one. 
P. Setia.—Anomia §., Gm. 8345, for Ch. f 714.—D. p. 297.— 
W. t.12, f. 80. —PLAcENTA Epuiprrum, Retz. p. 16.—P. S., Lam. 1. 
—E.t.174, f. 1.— Gray, Cat. Plac. 2.—Woodw. t.16, f.5. Flexuous, 
outline rather rhombic, but irregularly sinuous, being usually hollowed 
