OSTHEA. 
MOLLUSCA. OSTREAD^. 
m 
EXTINCT SPECIES. 
* Valves not plaited. 
1. O. gigantea — Depressed, longer than wide, pit of the hinge large, tri- 
partite, placed upon a straight perpendicular eminence, its sides flat, striated ; 
sides near the edge obscurely crenulated ; muscular impressions deep. — 
Brand. Foss. f. 88. Sower. Min. Conch . — London Clay. 
2. O. acuminata. — Depressed, very long, curved, with large subimbricated 
transverse waves beneath ; beaks and front acuminated. — Sower. Min. Conch, 
t. cxxxv. f. 2, 3 . — Lower Oolite. 
3. O. Depressed, very long, curved, two eared, a descending 
sinus or two in the anterior margin, near the front ; sides nearly parallel. — ■ 
Sower. Min. Conch, t. cxxxv. f. 1.— In Chalk. 
4. O. deltoidea — Equivalved, flat, thin, orbicular, ivith a sinus on one side, 
and a produced straight beak. — Sower. Min. Conch, t. cxlviii — Upper Oolite. 
5. O. escpansa. — Broad, deltoid, angles obtuse ; hinge-pit wide, flat, slightly 
elevated, and nearly straight ; cicatrix broad, with a sinus at the back. — 
Sower. Min. Conch, t. ccxxxviii. f. 1 . — Upper Oolite. 
6. O. undulata — Becurved, subtriangular, deep, posteriorly rounded ; sur- 
face radiated ; laminae imbricated, undulated ; cicatrix elongated, ovate, ob- 
lique ; hinge-pit slightly elevated. — Sower. Min. Conch, t. ccxxxviii. f. 2. — 
Plastic Clay. 
7. O Meadii — Tongue-shaped, thick, elongated, attached valve very con- 
cave, longitudinally undulated ; the other plain and ^diC— Sower. Min. Conch, 
t. cclii. f. 1, 4. — In Oolite. 
8. O. tener. — Depressed, elongated, thin, nearly plain ; attached valves 
nearly flat, with a canaliculated beak. — Sower. Min. Conch, t. cclii. f. 2, 3 
Plastic Clay. 
9. O. pulchra Orbicular, depressed ^ one valve nearly flat, with a short 
incurved beak ; the other valve convex, with numerous radiating undula- 
tions ; beak short ; hinge line straight ; laminae thin, close pressed. — Sower. 
Min. Conch, t. cclxxix.— Clay. 
10. O. bellovacina. — Thick, oblong, wedge-shaped, front rounded ; lower 
valve convex, composed of undulating laminae, the other flat and plain. Sower. 
Min. Conch, t. ccclxxxviii. f. 1, 2 — Plastic Clay. 
11. O. edulina . — Suborbicular or obovate ; lower valve rather concave, 
composed of undulating laminae ; the other smooth and flat ; beak pointed, 
curved. — Sower. Min. Conch, t. ccclxxxviii. f. 3, 4. — In Plastic Clay. 
12. O. IcBviuscula — Depressed, rounded, triangular ; surface obscurely im- 
bricated, smooth ; beak acute ; scales distinct. — Sower. Min. Conch, t. 
cccclxxxviii. f. 1 — In Lias. 
13. O. dbscura . — Oblong, uneven, small; lower valve very deep, the other 
flat ; beak curved — Sower. Min. Conch, cccclxxxviii. f. 2 — In Oolite. 
14. O. dorsata. — Convex, subimbricated ; upper valve marked with numer« 
ous longitudinal branched striae ; inner margin toothed.— .S'o^^/•cr. Min. Conch, 
t. cccclxxxix. f. I, 2 — London Clay. 
15. O. semiplana. — Oval, depressed, largely undulated; in the middle flat ; 
attachment small. Ostrea, Mant. Suss. 207- 1 . xxv. f. 4. — Sower. Min. Conch, 
t. cccclxxxix. f. 3 In Chalk. 
16. O. vesicularis — Subglobose, oblique, smooth, thin ; beak largely trun- 
cated; upper valve immersed, concave — Cuv. Oss. Foss. ii. t. iii. f. 5.-—Gry- 
phaea globosa. — Sower. Min. Conch, t. cccxcii. 
