1392 MOLLUSCA. OSTREAD.E. Ostrea. 



8. I. lulus — Valves convex near the beaks, flat and expanded towards the 

 front; surface marked with distant transverse ridges, and numerous concen- 

 tric stria? ; posterior slope smooth, depressed ? anterior side expanded ; hinge 

 oblique — ManL Suss. 216. t. xxvii. f. 10 In Chalk. 



9. I. Websteri — Convex, smooth, with distant, irregular, transverse ridges ; 

 beaks rounded, posterior slope nearly flat ; anterior side expanded ; hinge 

 very oblique. — Mant. Suss. 216. t. xxvii. f. 2 In Chalk. 



10. I. slriatus. — Gibbous, rounded, even, with numerous transverse strije ; 

 hinge oblique ? — Mant. Suss. 217- t. xxvii. f. 5 In Chalk. 



11. I. undulatus. — Convex, marked with numerous regular transverse ele- 

 vations and depressions ; posterior slope truncated ; hinge side expanded 



Mant. Geol. 217- t. xxvii. f. 6 In Chalk. 



OSTREADiE. 



Gen. XCVI.— OSTREA — Shell inequivalve, irregular, liga- 

 ment half internal, placed in a pit, which, in the fixed 

 valve, increases with age, as the upper valve is displaced 

 and advanced. 



5387. O. edulis. — Shell roundish-oval, with scaly foliations, 

 the upper valve less and flattened, the inner margin very en- 

 tire. 



Ostreum vulgar e, List. An. Aug. 176 — Conch, t. cxciii. — Linn. Syst. i. 

 11148. — Gregarious on a hard bottom. 



This shell varies much in size and shape, according to its locality. Oys- 

 ters are in season from September to April, during which period they are 

 procured by dredging, and eaten either in a raw or pickled state, or placed in ar- 

 tificial ponds, and fattened. They spawn in May, and the detached eggs, like 

 candle-drops, adhere to stones or other objects. Although oysters abound 

 in many parts of the coast, there are other places, especially among the 

 Hebrides, where the formation of productive beds could be easily executed 

 to advantage. 



. 388. O. parasitica. — Shell oblong, nearly smooth, the upper 



valve convex. 



Tuvt. Biv. Brit. 205. t. xvii. f. 6, 7 — Attached to different marine sub- 

 stances. 



Length seldom reaching two inches ; colour greenish, with longitudinal 

 brownish bands. In some cases, the upper valve is semicylindrically tumid, 

 and the under valve concave underneath, as if it had accommodated its shape 

 to a piece of stick of the size of the fore finger, with the beaks much incurved 

 on one side, and not extending beyond the margin. 



The Ostrea Crista-Galli, distinguished from our other recent species by its 

 triangular plaits, is sometimes round adhering to the bottom of foreign ves- 

 sels. ^Turt. Br. Brit. 204. 



