TRIBE 0STRACEA. 307 



O. Doridella. Lam. 35. — E. t. 188,/. 4, 5. Oblong, parasitical, 

 whitish, with about 4 good-sized plaits on each side : back flattened 

 and glabrous. 1^. Sumatra. 



O. Frons.— (Arg. t. 19,/. D.) — Mytilus F., Lin. Syst. p. 1155. — 

 Born, 193, vignette at p. 121,/. b.— D. p. 301.— W. t. 12,/. 3.— 0. F., 

 Ch. /. 680. — Hani. Conch. Mis. 0. f 5. — 0. Rubella, Limacella 

 and Erucella, Lam. 36, 37, 38. — 0. Folium, Reeve, Sys. t. 121,/. 3. 

 — 0. R, Cuvier, R. An. edit. Audouin, t. 72,/. 2. Very variable in 

 shape, being sometimes oboval, sometimes elongated oblong or sub- 

 fusiform, more or less solid, ranging in colour from purplish red to 

 orange-yellow, adorned with radiating rib-like folds, that usually 

 diverge, in the upper valve, from a more or less central dorsal rib, 

 and in the lower valve from a corresponding hollow (caused by the 

 Gorgonia, a stalk to which the shell has adhered by its hook-like 

 processes of attachment) : folds not imbricated or armed, usually 

 numerous, sometimes subangulated, sometimes obtuse, and generally 

 stronger in the lower valve. Inside of a paler or richer yellow; 

 inner margin of the upper valve rough with elevated granules : scar 

 moderate, lateral, more or less reniform. 2. W. Indies. The 

 O. Equestris of Say (Am. Con. t. 58) may prove the young of this 

 species. 



0. Folium. Lin. Mus. Ulr. p. 534.— Ch.f 665, 6.— E. t 184, 

 / 13, 4.— D. p. 274.— W. t. 11,/. 62,— (Knorr, 1, t. 23,/. 2.— Rump. 

 t. 47, / A. — Klein (copied) t. 8, / 22.) Oval, rather thin, purplish 

 brown, attached to a stick, which causes the upper valve to present a 

 more or less central elevated space corresponding with the cavity in 

 the lower valve ; sides obtusely and obliquely plaited ; surface not 

 lamellated : the edge not plicated, but simple : inside whitish or 

 displaying the external coating, subnacreous : margins not scabrous, 

 usually with a few granules near the cartilage. i X\. Indian Seas ? 

 I think that this species has been confused ivith many others, and 

 consequently have restricted the name to the shell described in the 

 Museum of Queen Ulrica. 



O. Labrella. Lam. 40. Small, wliitish, obliquely ovate, thin, 

 pellucid, broader at the base ; with a single row of oblique plaits ; 

 upper valve with prickly scales. ^. China and Japan. The type 

 in the French Museum reminds me of a young Folium armed with 

 incipient spiny tubercles, as iiv Hyotis. 



O. Plicata. Ch. 8, p. 34,/ 674, and Var.f 680.— D. p. 275.— 

 Lam. 41 (in part).-^E '. t. 184,/ 9.— W. 1. 11,/ Q3.—(Gualt. t. 104, 

 / A.) Very variable in shape, more or less longitudinally obovate, 

 peculiarly light and lamellar in structure, upper valve generally the 

 more convex, usually ashy with a purple tinge, purplish or rich 

 rufous (often radiated with lines of a deeper colour), with numerous 



