OSTREA. 



CONCHIFERA. 



145 



ed divergent striaj ; umbo flat ; part of tbo sides slightly cronu- 

 latod ; perforation very largo. 



Pleistocene Marino Formation, Ayr and Suffolk Crag. 



8. Ano.mia kadiata. — The Rayed Anemia, pi. LXVI.* 

 fig. 22. 



A. rad'mta. Sowerby, Goo. Trans. 2d Ser. IV. p. 338, 

 pi. 4, fig. 5. 



Flat, irregularly orbicular, with fine radiating striae. 

 Lower Greensand, Sandgate. 



9. Anomia squamula. — The Scaled Anomia, pi. LVII.* 

 fig. 16. 



A. sguamula. Brown, lUust. Rec. Conch. Brit. p. G9, 

 pi. 22, fig. 5. 



Suborbicular, very tbiu and flat, with indistinct concentric 

 wrinkles. 



Pleistocene Marine Formation, Ireland, and Coral Crag, 

 Mai ton. 



Genus XVll.—OST'REA.—LinncBus. 



Shell inequivalve, irregular, and foliaceous ; umbones some- 

 what separated, and of unequal size ; lower valve largest, 

 concave, and often adherent ; upper valve smallest, and some- 

 what plain ; hinge destitute of teeth, but sometimes slightly 

 crenated on the anterior side near the beaks ; ligament partly 

 external ; the facet to which it is attached subtrigonal and 

 tripartite, and divided by two elevated lines which divaricate 

 from the umbo ; each valve provided with two muscular im- 

 pressions, the one large, suborbicular, and nearly central ; 

 the other very small and situate near the hinge. 



1. OsTUEA acuminata. — The Acuminated Oyster, pi. 

 LVII. fig. 2, 3. 



0. acuminata. Sowerby, II. p. 81, pi. 35, figs. 2, .3. 



Much elongated, depressed, and incurved ; upper valve a 

 little concave, and rather smooth ; distinctly eared, and with 

 rather acute umbones ; base acuminated ; surface with largo 

 subimbricated transverse undulating lamina;. 



Fuller's Earth, Bathford Hill, Great Oolite, Stonesfield 

 and Cain's Cross ; Inferior Oolite, Limpley Stoke. 



2. OsTREA CANALICDLATA. — The Caualed Oyster, pi. 

 LVII. fig. 9. 



0. catialiculata. Sowerby, II. p. 81, pi. 35, fig. 1. 



Depressed, much elongated, curved, slightly and equally 

 eared ; one or two descending sinuses in the anterior margin 

 near the base ; sid(^ almost parallel, posterior side fequeutly 

 gaping ; near the beak a few concentric lamina;, and two or 

 more canaliculated projections in the lower valve, which is 

 more convex than the other ; upper valve flat. 



Upper Chalk, Lewes and Norwich. 



3. OsTREA Bellovacina. — The Bellovian Oyster, pi. 

 LVII. fig. 1. 



0. Belorncina. Lamarck, An. du Mus. VIII. pi. 159, 

 and XIV. pi. 20, fig. 1. Deshayes, Coq. Fos. pi. 48, fig. 12. 

 lb. Ann. San. Vert. VI. pt. 1, p. 228. Sowerby, IV. p. 121, 

 pi. 388, figs. 1, 2. 



Oblong ; form irregular, somewhat orbicular or wedge-shap- 

 ed, thick ; lower valve convex, composed of undulating, sub- 

 imbricated lamin:c ; beak considerably produced, and straight 



on each side ; ligamental area, a little elevated above the sur- 

 face of the shell ; in the hollow valve it is curved and acute, 

 with a deep canal in the middle. 



Plastic Clay, Phumstead, Woolwich, Reading, Headley. &c. 



4. Ostrea EDULiNA. — The Small Edible Oyster, pi. LVII. 

 fig. 15. 



0. cdulina. Lamarck, An. San. Vert. VI. pt. 1, p. 218. 

 Sowerby, IV. p. 122, pi. 388, figs. 3, 4. 



Suborbicular, or subovate ; moderately thick ; lower valve 

 convex, composed of undulating lamina; ; upper valvo very 

 smooth and depressed ; beak curved and pointed ; but desti- 

 tute of straight lines on its sides. 



Plastic Clay, Charlton and New Cross. 



5. Ostrea l^viuscula. — The Very Smooth Oyster, pi. 

 LVII. fig 13. 



0. Iwvluscida. Sowerby, V. p. 143, pi. 488, fig. 1. 



Depressed, rounded, or somewhat triangular, beak subacute 

 and retroflected ; scales distant ; surface smooth and obscurely 

 imbricated ; lower valve destitute of ribs. 



Kimmeridge Clay, Aylesbury and Bedford. 



6. .Ostrea costata. — The Ribbed Oyster, pi. LVIII. fig. 9. 

 0. costata. Sowerby, V. p. 143, pi. 488, fig. 3. 

 Suborbicular, lower valve with numerous furcated and 



doubly furcated divergent ribs ; upper valve flat, with an 

 undulated margin ; beak obscure. 

 Great Oolite, Hampton and Ancliff. 



7. Ostrea obscura. — The Obscure Oyster, pl.LIX. figs. 3, 4. 

 Sowerby, V. p. 143, pi. 488, fig. 2. 



Oblong; irregular; beak obtuse and curved; hinge area 

 large, triangular ; lower valve very deep, the other flat. 

 Great Oolite, Ancliff, AViltshire. 



8. Ostrea dorsata. — The Backed Oyster, pi. LIX. fig- 2. 



0. dorsata. Sowerby, V. p. 144, pi. 489, figs. 1, 2. Des- 

 hayes, Coq. Fos. I. pi. 53, figs. 9, 10, 11, and pi. 64, figs. 1, 

 2, 3, 4. 



Oblong ; form variable ; convex ; beaks blunt ; upper valve 

 very convex, with numerous longitudinal subimbricated, many- 

 branched stria; ; inner margin toothed. 



London Cl.av, Barton. 



9. Ostrea semiplaxa. — The Half-plain Oyster, pi. LIX. 

 fig. 7. 



0. semiplana. Sowerby, V. p. 144, pi. 489, fig. 3, Man- 

 till, Geo. Suss. p. 207, pi. 25, fig. 4. 



Oval ; depressed ; surface largely foliated ; valves flat in the 

 middle ; edges free from deep sinuations. 



Upper Chalk, Gravcsend, Lewes, and Wiltshire. 



1 0. Ostrea deltoidea. — The Deltoidal Oyster, pi. LIX. 

 fig. 10. 



0. deltoidea. Lamarck, Env. de Paris, p. 265. Sowerby, 

 IV. p. Ill, pi. 148. 



Equivalve, thin, flat, much compressed, triangular ; laminar ; 

 beaks equal, much produced, and straight, and pointing on 

 one side ; one side with a deep sinus ; edges extending con- 

 siderably beyond the enamelled surface of the interior, giving 

 the external contour a more rounded aspect than the internal. 



Kimmcridfro Clay, Portland, Weymouth, and counties of 

 Buckingham, Bedford, and York. 



11. Ostrea expansa. — The Expanded Oyster, pi. LVIII. 



fig. r. 



2n 



