392 
MOLLUSCA. OSTREAD7E. 
OSTREA. 
8. 1. latus — Valves convex near the beaks, flat and expanded towards the 
front ; surface marked with distant transverse ridges, and numerous concen- 
tric striae ; posterior slope smooth, depressed ? anterior side expanded ; hinge 
oblique — Mant. Suss. 216. t. xxvii. f. 10 In Chalk. 
0. I. Wehsteri — 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 striae ; 
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. 
OSTREAD.^. 
Gex. 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, 
387. O. edulis . — Shell roundish-oval, with scaly foliations, 
the upper valve less and flattened, the inner margin very en- 
tire. 
Ostreum vulgare. List. An. Ang. 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, fattened. They spawn in May, and the detached eggs, like 
candle-drops, adhere to stones or other objects. Although oy.sters 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. 
Turt. 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 Crisla-Gall% distinguished from our other recent species by its 
triangular plaits, is sometimes found adhering to the bottom of foreign ves- 
,sels Turt. Br. Brit. 204. 
