296 TESTACEOUS MOLLUSCA. 



—Da Cost. t. 11,/. 6.— Crouch, t. 12, /. 8.— Cone. Man. /. 180.— 

 W. t. 11,/ 74.— Brit. Mol.—O. Parasitica, Turt. Die. p. 134,/. 8 ; 

 Biv. p. 205, t. 17,/. 6, 7. Obovate, inequivalve, rounded and some- 

 what dilated at the base, narrower at the apex, where, in the lower 

 valve, there is a tendency to dilate and form a crest-like process at 

 the sides ; upper valve the less solid, very shallow, covered with 

 numerous imbricated concentrically arranged loose flakes, which are 

 pale ashy brown, undulated, yet scarcely raised ; lower valve white, 

 strong, not so shallow, armed with radiating ribs that are crossed by 

 rather elevated distant concentric lamellae, which are vandyked by the 

 intersection of the ribs ; edges somewhat wavy, yet not at all plicated, 

 neither scabrous nor crenated, but marked, for the most part, in the 

 vicinity of the hinge-margin, with more or less closely disposed linear 

 denticles, which run parallel to it. 4. Britain, Sc. — Var. ? 0. E. ? 

 var. Purpurea, Conch. Mis. O.f. 8. Both valves purplish chocolate, 

 not variegated, not thick ; flakes of the upper valve glossy, undulated, 

 very loose, not erect, those of the lower valve distant, very loose, 

 curly, more or less elevated, here and there almost foliaceous ; beaks 

 acute ; interior slightly tinged with external colouring ; cartilage 

 conical ; cardinal denticles indistinct. Toulon, attached to a stake. 



0. Hippopus. Lam. 2. — Desh. E. 2, p. 288. Large, thick, round ; 

 upper valve flat; the concentric lamellae very numerous and de- 

 pressed. 5. Boulogne.* 



O. Adriatica. Lam. 4. — Phil, in Kust. Ch. vii. 1, 1. 13,/. 1, 2, 3. 

 — Mid. Mai. Bos. 3, p. 6. — 0. Taurica, Kryn. Bui. Nat. Mosc. 20 

 (1837), t. 3, teste Mid. Subtriangular, peaked at the beaks, dilated 

 below, compact, not thick, margin usually straight on one side, and 



1 I have given a translation of Lamarck's description, but, judging 

 from his specimen in the Museum, consider the shell to be merely a 

 coarse variety of Edulis with the cardinal denticulations distinct and 

 the lamellae of the upper valve obsolete. M. Deshayes has given the 

 following more detailed account of the species : — " Rounded-oval, 

 thick but light, irregular, both valves covered with concentric lamellae, 

 which scarcely project, and are furnished with many folds, especially 

 towards the margin : lower valve larger, thicker, more tumid, and 

 provided with longitudinal ribs, that are traversed by concentric scaly 

 lamellae : inside quite white, having slight bump-like elevations or 

 undulations : scar semilunar, larger in proportion than in Edulis, 

 more laterally situated : beaks always broad and produced, that of the 

 lower valve deeply hollowed by a moderately sized canal, which is 

 margined on each side by a decurrent varix-like projection, that of 

 the upper valve flatter, with both varices and canal nearly obsolete." 



