146 



CONCHIFERA. 



OSTREA. 



0. expansa. Sowerby, III. p. 65, pi. 238, fig. 1. 



Broad ; length and breadth nearly equal ; deltoidal, with 

 obtuse angles ; beaks obscure, hinge area wide, flat ; slightly 

 elevated, and nearly straight ; cicatrix broad, with a sinus at 

 the beak ; margin with large undulations, surface laminar ; 

 muscular impressions very large and deep. 



Portland Sand, Whitchurch ; Quainton, Buckinghamshire ; 

 Wiltshire and Bedfordshire. 



12. OsTREA UNDULATA. — Tho Waved Oyster, pi. LVIII. 

 fig. 6. 



0. undulata. Sowerby, III. p. 65, pi. 238, fig. 2. 



Subtriangular, recurved, convex, and rounded posteriorly ; 

 thick ; beaks blunt ; surface with many longitudinal depressed 

 ribs, and shallow intervening furrows, with numerous distant, 

 undulating, imbricated lamina; ; cicatrix elongated, ovate, and 

 oblique ; hinge pit slightly elevated. 



Portland Sand, Vale of Wardour. 



13. OsTREA PLABELLULA. — The Little Fan Oyster, pi. 

 LVII. figs. 11, 12. 



O. Jiahellula. Sowerby, III. p. 97, pi. 253. 0. cj/nihiila. 

 Lamarck, An. San. Vert. VI, pt. 2, p. 215. 0. chania pli- 

 cata. Brander, p. 36, pi. 7, fig. 84, 85. Deshayes, pi. 63, 

 figs. 5, 6, 7. 



External form very variable, oblong, and always subarcuated ; 

 beaks prominent, that of the larger valve nmch curved ; larger 

 valve deep, longitudinally and irregularly curved and plaited, 

 with the margin dentated ; smaller valve flat, smootii, with 

 remote imbricated lamina j margin plain ; the lateral crenu- 

 lations are well marked, on the sides and margin of the flat 

 valve near the hinge. 



London Clay, Barton and Bracklesham. 



\i. OsTREA TENERA. — The Tender Oyster, pi. LVII. fig. 14. 



O.Jener. Sowerby, III. p. 95, pi. 252, figs. 2, 3. 



Much elongated, slightly curved, thin, dei)ressed ; beak of 

 the upper valve acute, and included in the frequently curved 

 beak of tho uuder valve, and canaliculated ; surface almost 

 plain and smooth, with obsolete imbricated laminae. 



Plastic Clay, Woolwich. 



15. OsTREA Meadii. — Mcade's Oyster, pi. LVIII. fig. 3. 

 0. Meadii. Sowerby, III. p. 95, pi. 252, figs. 1 — 4. 

 Much elongated, thick ; hinge area large, the pit wide ; 



beaks projecting ; attached valve very deep, and longitudin- 

 ally rugged and undulated ; the other plain and flat, with 

 lateral crenulations near the hinge ; edges very irregular. 

 Great Oolite, Somersetshire. 



16. OsTREA GiGANTEA. — The Gigantic Oyster, pi. LVII. 

 fig. 4. 



0. gigantea. Brander, p. 37, pi. 8, fig. 88. Sowerby, I. 

 p. 143, pL 64. 



Slightly elongated, very thick, irregular in form, umbo 

 short, very little incurved ; hinge-pit large, tripartite, situ- 

 ated upon a slightly oblique elevation, with its sides flat and 

 striate<l, and its internal end perpendicular to the surface of 

 the valves, and not gradually curved into the sides of tho 

 shell, as in other species. 



This shell is very large, frequently measuring upwards of seven and 

 a half mches, and weighing two to three pounds. 



L(mdon Clay, Barton and Bognor. 



17. OsTREA PULCHRA. — The Fine Oyster, pi. LIX. fig. 12. 



0. pulckra. Sowerby, III. p. 141, pi. 279. 



Nearly orbicular, compressed ; one valve convex, with an 

 obscure beak, and numerous radiating flat ribs and shallow 

 furrows, crossed by wide-set undulating lamina; ; the other 

 valve almost flat, with a short, blunted, slightly incurved 

 beak ; hinge-line parallel. 



Plastic Clay, Woolwich and Sundridge. 



18. OsTREA soLiTAUiA. — Tho Solitary Oyster, pi. LIX. 

 figs. 8 and 11. 



0. solitaria. Sowerby, V. p. 105, pi. 468, lig. 1. 0. pul- 

 ligera. Goldfuss, pi. 72, fig. 11 ? 



Obovate, thick ; sometimes incurved ; beaks short ; surface 

 wit!) many divergent strong and frequently furcated ribs, and 

 deep intervening furrows, crossed by elevated rugged imbri- 

 cated laminoB ; one valve flatter than the other. 



Portland Stone, Dunton, Bucks ; and the Coral Rag, 

 Mai ton. 



19. OsTREA MACROPTERA. — The Long Winged Oyster, 

 pi. LVIII. figs. 1, 2. 



0. macroptera. Sowerby, V. p. 105, pi. 468, figs. 2, 3. 

 Parkinson, III. pi. 14, figs. 4. 



Falciform, compressed, with a large rectangular wing within 

 the curve ; surface with irregular, undulating, deep plaits ; 

 deeply furrowed and acutely ribbed towards the margin of 

 the valves, producing a sories of deep and sharp tooth-like 

 processes, locking into each other ; hinge area wide, triangu- 

 lar, the pit for the ligament broad and much incurved ; beaks 

 long, incurved and pointed. 



Gualt, Folkstone, and Lower Greensand, Atherfield and 

 Berehead. 



20. OsTREA CARINATA. — The Keeled Oyster, pi. LIX. 

 fig. 6. 



0. carinata. Lamarck, VI. pt. I. p. 216, Ency. Meth. 

 pi. 187, figs. 3, 4, 5. Goldfuss, Pet. pi. 74, fig. 6. Sowerby 

 IV. p. 89, pi. 365. 



Elongated, arcuated, irregular and much inflated, and point- 

 ed at both extremities ; sides flattened ; whole surface with 

 numerous transverse deep furrows, and strong elevated angu- 

 lar sharp ribs ; the centre with a keel ; margin with strong 

 deep tooth-like processes locking into each other. 



Chalk Marl, Dover and Lyme Regis ; Upper Greensand, 

 Chute Farm, and Southbourn ; Lower Greensand, Kent and 

 Isle of Wight. 



21. OsTREA Marshii. — Marsh's Oyster, pi. LIX. 

 fig. 10. 



0. Marshii. Sowerby, I. p. 103, pjt 48. Goldfuss, pi. 

 73. 0. diluviana. Parkinson, III. pi. 15, fig. 1. 



Longitudinal, oblique, compressed, beak obscure ; obscurely 

 eared, 7 or 8 angular, large, obliquely longitudinal ribs and 

 furrows, crossed by concentric, zigzag, undulating lamina; ; edge 

 thick, with strong and very deep-set triangular tooth-like 

 processes locking into each other. 



Middle Oolite, Yorkshire and Wiltshire ; the Inferior Oolite, 

 Yorkshire and Gloucestershire. 



22. OsTREA GREGARIA. — The Gregarious Oyster, pi. LVII. 

 fig. 10. 



0. gregaria. Sowerby, II., p. 19, pi. III. fig. 1. 

 Clustered, oblong, generally curved ; substance of the shell 

 thin, especially towards the edges ; beaks long, very slightly 



