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. Bed Sea; Australia. 



V. Hians. [Gualt. t. 90, /'. H.) — Mya Vulsella, young, Ch. 

 f. 10. — V. H., Lam. 3.— (f Sav, Egy. t. 14, /. 3.) Oblong, sub- 

 arcuated, tumid, brown with paler radiating lines : gaping on both 

 sides, especially the hinder one. 2£. Indian Ocean. 



V. Rugosa. Lam. 3. — Del. t. 18, /. 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. Spongiarum. Lam. 4. — . ? Mya Vulsella Minor, Ch.f. 8, 9, 

 copied E. t. 178, f. 5. Oblong, straight, somewhat attenuated near 

 the beaks, with concentric wrinkles, the longitudinal ones obsolete : 

 internal nacre with a violet tinge. If. Indian Ocean. The epi- 

 dermis thin, greyish and longitudinally ivrinkled. 



V. Mytilina. Lam. 6. Large, elongated, white, but with the 

 vestiges of darker radiating lines, with merely the wrinkles of 

 increase ; valves convex, attenuated near the hooked beaks, flattened 

 and dilated at the opposite extremity. 5. Perchance a bleached 



LlNGULATA. 



V. Ovata. Lam. 6. Oval-elliptic, rather depressed, somewhat 

 violet, never rayed ; with merely concentric lines of increase : nacre 

 pearly, ly. Australia. 



V. Nuttallii. Conr. Jour. Ac. N. 8. Phil. 7, p. 257, t. 20,/. 10. 

 Very irregular, with concentric lamellar striae 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 . . . ^. Friendly 

 Isles. Possibly a distorted specimen. 



PLACUNA. 



Shell free, subequivalve, irregular, very flat ; hinge consisting, in one 

 valve, of two short longitudinal convergent ?ibs, in the form of the 

 letter V placed upside down, which fit into two corresponding cartilage- 

 grooves in the opposite one. 



P. Sella.— Anomia S., Gm. 3345, for Ch.f. 714.— D. p. 297.— 

 W. t. 12, f. 30. — Placenta Ephippium, Retz. p. 16. — P. S., Lam. 1. 

 — E. 1. 174,/. I.— Gray, Cat. Plac. 'X.— Woodw. 1. 16,/ 5. Flexuous, 

 outline rather rhombic, but irregularly sinuous, being usually hollowed 



