OsTREA. MOLLUSCA. OSTREAD^E. 393 



EXTIXCT SPECIES. 



" Valves not plaited. 



1. (J. giyantca. — Depressed, longer than wide, pit of the hinf^fe large, tri- 

 ])artite, placed upon a straight perpendicular eminence, its sides flat, striated ; 

 sides near the edge obscurely crenulated ; muscular impressions deep. — 

 Brand. Foss. f. 88. Sower. 3Iin. Conch — London Clay. 



2. O. acuminata, — Depressed, very long, curved, wLtli large subimbricated 

 transverse waves beneath ; beaks and front acuminated — Sower. Min. Conch, 

 t. cxxxv. f. 2, 3- — Lower Oolite. 



3. O. canaliculata. — 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, with a sinus on one side, 

 and a produced straight beak — Sower. Min. Conch, t. cxlviii — Upper Oolite. 



5. O. expansa. — 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. 



C. O. undulata Recurved, subtriangular, deep, posteriorly rounded ; sur- 

 face radiated ; laminre imbricated, undulated ; cicatrix elongated, ovate, ob- 

 lique ; hinge-pit slightly elevated — Sower. Min. Conch, t. ccxxxviii. f. 2 



Pl'stic Clay. 



7. O Meadii — Tongue-shaped, thick, elongated, attached valve very con- 

 cave, longitudinally undulated ; the other plain and ^aX.— 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. pnlchra — 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.— 5'ower. 

 Min. Conch, t. cclxxix.— P/as<Jc 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. laviuscula. — Depressed, rounded, triangular ; surface obscurely im- 

 bricated, smooth ; beak acute ; scales distinct. — Sower. Min. Conch, t. 

 cccclxxxviii. f. 1 — In Lias, 



13. O. ohscura.— 0\Aox\g, 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. — iSower. Min. Conch, 

 t. cccclxxxix. f. 1, 2 — London Clay. 



15. O. semiplana — Oval, depressed, largely undulated ; in the middle flat ; 

 attachment small. Ostrea, Mant. Suss. 207! t. xxv. f. i.— 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. 



