OsTREA. 
CONCHIFERA. 
147 
incurved ; binge-pit with a central cavity in the lower valve 
and a corresponding projection in the upper one; one valve 
considerably 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 laminae. 
Coral Rag, Malton, Wiltshire, and Calcareous Grit, Scar¬ 
borough and Upware. 
23. Ostrea duriuscula.—T he Ragged Ostrea, pi. L1X. 
fig. 1. 
0. duriuscula. Phillips, Geo. York, I. p. 101, pi. 4, fig. 1. 
Obliquely 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. Ostrba injf.qualis.—T he Unequal Oyster, pi. LIX. 
fig. 5. 
0. incequalis. Phillips, Geo. York, I. p. 109, pi. 5, fig. 13. 
Surface extremely rugged, and the margins irregularly 
undulated ; lines of growth waved. 
Oxford Clay, Scarborough, Yorkshire. 
25. Ostrea undosa.—T he Waved Oyster, pi. LVIII. 
fig. 4. 
0. undosa . Phillips, Geo. York, I. p. 112, pi. G, 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. 
Kollo ways Rock, Scarborough, Yorkshire. 
2G. Ostrea arclietypa.—T he Original Ostrea, pi. LVIII. 
fig. 5. 
0 . arclietypa. Phillips, Geo. York, I. p. 112, pi. G, fig. 9. 
Umbo placed near to one side, and somewhat obtuse; a 
largo wide furrow emanating from the disc, increasing as it 
descends to the base; and a narrower ono in front, general 
contour of the shell oblique, with the margins undulated. 
Kelloways Rock, Scarborough and Wheatcross. 
27. Ostrea palmetta.—T he Palmated Ostrea, pi. LXI.* 
figs. 3, 4. 
0. palmetta. Sowerby, II. 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. 
Differing from 0. gregaria in being flatter, with the plates 
fewer and more irregular. 
Great Oolite, Marston, near Oxford. 
28. Ostrea aljEformis.—W ing-shaped Ostrea, pi. LXI.* 
figs. 1, 2. 
0. alaformis. Woodward, Geo. Xor. p. 48, pi. G, figs. 
1, 2, 3. 0. serrata. Brongniart, Env. de Paris, pi. 3, fig. 10. 
Wing-shaped ; umbo situate near one side, which is very 
short, the other side extending laterally, and 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. LXVI.** 
figs. 23, 24. 
O. distorta . Sowerby, Geo. Trans. 2d Ser. IV. p. 34G, pi. 
22, fig. 2, Ann. of Phil. N. S. VIII. p. 379. 
Elongated, narrow towards the hinge ; ono valve quite flat; 
surface of both valves smooth. 
Purbeck, Lowth, Wiltshire, and Portland Sand, Buckingham. 
30. Ostrea edulis. —The Edible Ostrea. 
O. edulis. Brown, III. Rec. Conch., p. 71, pi. 30,* figs. 6, 7. 
Form variable, generally roundish oval, upper valve flat, with 
transvorse scaley foliations; the under valve convex, and the 
inner margin entire. 
The Pleistocene Marino Formation, Renfrewshire, and the 
Coral Rag, Ramsbot, and common many other places. 
31. Ostrea falcata. —The Hooked Ostrea, pi. LXVI.** 
G, 7, fig. 27. 
O. falcata. Sowerby, 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 ix/equicostata. —The Unequal-ribbed Ostrea, 
pi. LXI.* fig. 13. 
O. incsquicostatus. Woodward, Geo. Nov. p. 08, pi. G, fig. 4. 
Obliquely quadrangular, umbo placed much to ono side; 
hinge-line nearly parallel; surface with many unequal ribs; 
margins plicated. 
Upper Chalk, Harford Bridge, Norfolk. 
33. Ostrea lateralis. —The Lateral Ostrea, pi. LXI.* 
figs. 5-8. 
O. 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. 
LXI * figs. 20, 21. 
O. 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 retusa.— The Blunt Ostrea, pi LXVI ** 
fig. 28. 
O. return. Sowerby, Geo. Trans., 2d Ser. IV p 328 nl 
14, fig. 4. 
Form exceedingly variable, but for the most part orbicular 
and greatly curved; moderately thick, plain in the middle, 
but furnished with angular plaits on the margin. It occurs in 
masses. 
Lower Greensand, Artherfield, Isle of Wight. 
3G. Ostrea sdlcipera—T he Furrowed Ostrea nl 
LXI.* figs. 30, 31. 
O. mlcifera. Phillips, Geo. York, I. p. J23, nl <1 
fig. 35. _ ’ 
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 
