OsTREA. 



CONCHIFEKA. 



147 



incurved ; binge-pit with a central cavity in tlie lower valve 

 and a corresponding projection in the upper one ; one valve 

 cousidcraldy deeper than the other ; surface with a broken 

 longitudinal plait or furrow, from which diverge numerous 

 irregular sharp, frequently furcated or branched ribs, crossed 

 by imbricated laininsB. 



Coral Rau', ]Malton, Wiltshire, and Calcareous Grit, Scar- 

 borough and Upware. 



23. OsTREA DURiuscDLA. — The Ragged Ostrea, pi. LIX. 



fig- 1. 



0. diiriuxcula. Phillips, Geo. York, I. p. 101, pi. 4, fig. 1. 



Oblicjuely ovate ; hinge with a produced auriform process on 

 one side ; surface with rude irregular longitudinal wrinkles 

 and concentric lines of growth. Length 2 inches. 



Coral Rag, Malton ; and near Scarborough, Yorkshire. 



24. OsTRKA iNJEQCALis. — The Une(|ual Oyster, pi. LIX. 

 fig. 5. 



0. inaqualis. Phillips, Geo. York, I. p. 109, pi. 5, fig. 1.5. 

 Surface extremely rugged, and the margins irregularly 

 undulated ; lines of growth waved. 



Oxford Clay, Scarborough, Yorkshire. 



25. OsTREA UNDOSA. — The Waved Oyster, pi. LVIIL 

 fig. 4. 



0. undosa. Phillips, Geo. York, L p. 112, pi. 6, fig. 4. 



Obliquely ovate, umbones nearly central ; sides near the 

 hinge almost even, on one side an indistinct longitudinal 

 furrow reaching two-thirds of the length from the basal mar- 

 gin ; the other side with a series of obliquely transverse, pretty 

 strong, nearly equidistant undulations. 



Kelloways Rock, Scarborough, Yorkshire. 



26. OsTREA ARCHETYPA. — The Original Ostrea, pi. LVIII. 

 fig. 5. 



0. archetypa. Phillips, Geo. York, I. p. 112, pi. 6, fig. 9. 



Umbo ydaced near to one side, and somewhat obtuse ; a 

 large wide furrow emanating from the disc, increasing as it 

 descends to the base ; and a narrower one in front, general 

 contour of the shell oblique, with the margins undulated. 



Kelloways Rock, Scarborough and Wheatcross. 



27. Ostrea palmetta. — The Palmated Ostrea, pi. LXL* 

 figs. 3, 4. 



0. palmetta. Sowerby, IL p. 20, pi. 111. fig. 2. 



Oblong-ovate, depressed ; umbo .straight, nearly central, 

 slightly turned to one side, and a little curved ; with a single 

 obscure ear ; a longitudinal space running from the umbo to 

 the base, from which diverge numerous blunt, oblique ribs ; 

 margins plaited. 



Diir.'ring from 0. ^re^aria in being flatter, with the plates 

 fewer and more iiTegular. 



Great Oolite, Marston, near Oxford. 



28. Ostrea al.«:formis. — Wing-shaped Ostrea, pi. LXL* 

 figs. !, 2. 



0. nltpformif. AVoodward, Geo. Nor. p. 48, pi. G, figs. 

 1, 2, 3. 0. gerrata. Brongniart, Env. de Paris, pi. 3, fig. 10. 



Wing-shaped ; umbo situate near one side, which is very 

 short, the other side extending laterally, ami is five times the 

 dimensions of the other side ; a nearly central space from the 

 umbones, from which diverge numerous ribs ; margins with 

 numerous plaits, and with a horizontal frill extending to a con- 

 siderable extent, valves very irregular in form. 



Upper Chalk, Norwich. 



29. Ostrea distorta.— The Distorted Ostrea, pi. LXVL" 

 figs. 23, 24. 



0. distorta. Sowerby, Geo. Trans. 2d Ser. IV. p. 34G, pi. 



22, fig. 2, Ann. of Phil. N. S. VIII. p. 376. 



Elongated, narrow towards the hinge ; one valve quite flat ; 

 surface of both valves smooth. 



Purbeck, Lowth, Wiltshire, and Portland Sand, Buckingham. 



30. Ostrea edulis. — The Edible Ostrea. 



O. edulis. Brown, 111. Rec. Conch., p. 71, pi. 30,* figs. 6, 7. 



Form variable, generally roundish oval, upper valve flat, with 

 transverse scaley foliations ; the under valve convex, and the 

 inner margin entire. 



The Pleistocene Marine Formation, Renfrewshire, and the 

 Coral Rag, Ramshot, and common many other places. 



31. Ostrea falcata.— The Hooked' Ostrea, pi. LXVL** 

 6, 7, fig. 27. 



0. falcata. Sowerbv, Geo. Trans. 2d Ser. IV., p. 347, pi. 



23, fig. 1. 



Considerably elongated and curved towards the posterior 

 side ; one valve flat and thick, surface with numerous foli- 

 .ations, the characters of the other valve unknown. 



Portland Sand, Chicksgrove and Swindon. 



32. Ostrea injjquicostata.— The Unequal-ribbed Ostrea 

 pi. LXL* fig. 1.3. 



0. inaiquicostatus. Woodward, Geo. Xov. p. 68, pi. 6, fig. 4. 



Obliquely quadrangular, umbo placed much to one side; 

 hinge-line nearly parallel ; surface with many unequal ribs ; 

 margins plicated. 



Upper Chalk, Harford Bridge, Norfolk. 



33. Ostrea lateralis.— The Lateral Ostrea, pi. LXL* 

 figs. 5-8. 



0. lateralis. Goldfuss, pi. 82, fig. 1. 



Oblong-ovate, incurved, anterior beak involute ; the upper 

 valve with concentric lineations; the lower valve plain, with 

 deep foliations attached by the beak. 



The Chalk, Norfolk. 



34. Ostrea lunata.— The Crescent-shaped Ostrea, pi. 

 LXL* figs. 20, 21. 



0. lunata. Goldfuss, pi. 75, fig. 2. 



Equivalve, oblong, crescent-shaped, with the surface and 

 margins undulating and smooth ; posterior side triangular 

 In the chalk ? 



35. Ostrea retcsa.— The Blunt Ostrea, pi LXVI »* 



fig. 28. 



0. retusa. Sowerby, Geo. Trans., 2d Ser. IV p 32.S ,,1 

 14, fig. 4. f • 1 • 



Form exceedingly variable, but for the mc.st part orbicular 

 and greatly curved ; moderately thick, i>l;;in in the middle, 

 but furnished with angular plaits on the margin. It occurs in 

 masses. 



Lower Grecnsand, Artherfield, Isle of Wight. 



30. Ostrea sulcifera.— The Furrowed Ostrea, i>l 

 LXL* figs. 30, 31. ' ' 



0. sulcifera. Phillips, Geo. York, I. p. 123 pi n 

 fig. 35. » ' F-, 



Oblong-ovate, inflated, umbones nearly central, from whence 

 emanates a broad central furrow in both valves, which ter- 

 minate at the base of the valves; several indistinct oblique 



