PISCIDILJM. 
CONOHIFERA. 
Transversely wedge-sLaped; anterior side considerably 
angulated ; surface with numerous fino lines of growth. 
The Plastic Clay, Charlton, Upnor, Plumstead, and New- 
cross. 
5. Cyrena obovata.— The Egg-ovate Cyrena, pi. 
LXXXYI. fig. 1 . 
Cyclas obovata . Sowerby, II. p. 140, pi. 102 , figs. 4, 5, 0. 
Obovato, length and breadth equal; gibboso ; anterior side 
obtuse ; beaks largo; surface with rather strong, irregular 
lines of growth. 
Upper Marl, Colwell Bay, and Barton. 
0 . Cyrena pxjlchra. —Tho Beautiful Cyrena, pi. 
LXXXIII. fig. 30. 
Cyclas pulcher. Sowerby, VI. p. 51, pi. 527, fig. 1. 
Sub-orbicular, convex; posterior side truncated ; surface 
smooth ; hinge with one sharp-edged and two bifid teeth ; 
lateral teeth obtuse and plain ; substance thin and slender. 
Tho Upper Marl, Hampstead Cliff and Isle of Wight. 
Genus XXXIV.—CYCLAS.— Brugulire. 
Shell generally sub-orbicular; ventricose, equivalve, nearly 
equilateral, transverse, and thin, covered with a delicate oliva¬ 
ceous epidermis; two very minute, divergent, cardinal teeth 
in both valves, one of which is double in tho left one ; lateral 
teeth two, remote and a little elongated, laminar, compressed, 
and acute; and four in the other, two of which are very small, 
situato on oach side of the hinge; two lateral ovate muscular 
impressions in both valves, that of the mantle entire, and des¬ 
titute of a sinus; ligament external and slender. 
1 . Cyclas media (?.)—The Middle Cyclas, pi. LXXXVI. 
fig. 14. 
C. medius. Sowerby, p. 51, pi. 527, fig. 2 . 
Depressed, thick, transversely obovato ; anterior side small, 
posterior side somewhat pointed ; surface smooth ; one tooth 
under the beaks in both valves. 
Tho Weald, of which it is tho characteristic, Kent, Sussex, 
and Surry. 
2 . Cyclas membranacea. —Tho Membranaceous Cyclas, 
pi. LXXXVI. fig. 28. 
C. membranacea . Sowerby, VI. p. 52, pi. 527, fig. 3. 
Depressed; very thin ; transversely ovate; anterior side 
small; posterior side a little pointed. 
Tho Weald, Dorset, Sussex, and Wiltshire. 
8 . Cyclas angulata. —The Angular Cyclas, pi. LXXVI. 
fig. 6. 
C. angulata. Sowerby, Geo. Tr. 2dJ3er. IV. pi. 21, f. 12 . 
Sub-triangular; beaks prominent; anterior side rounded, 
posterior side truncated; its line from tho beaks to the trun¬ 
cation nearly straight; surface smooth, with shallow lines of 
growth. 
Tho Weald, Sussox, tho Isle of Purbeck; and South Wilt¬ 
shire. 
4. Cyclas sub-quaduata. —Tho Half-square Cyclas, pi. 
LXXXVI. fig. 13. 
C. sub-quadrata. Sowerby, Geo. Tr. 2 d Ser. IV. pi. 21 , 
fig. 8 . 
Transversely elongated; an oblong square; both sides 
200 
nearly straight; beaks central and small; back and base 
straight and parallel; surface witii strong concentric furrows. 
Tho Weald Hastings, and St Leonards. 
5. Cyclas elongata.—T he Elongated Cyclas, pi. 
LXXXVI. fig. 1 2. 
C. elongata . Sowerby, Geo. Tr. 2 d Ser. IV. pi. 21 , fig. 9. 
Transversely elongated; beaks nearly central; anterior 
side rounded, posterior side obliquoly truncated, and angular 
above, rounded beneath; dorsal and basal lines nearly straight 
and parallel ; surface smooth, with three or four distinct lines 
of growth. 
Tho Weald, Sussex, and tho Purbock Beds, Whitchurch 
and Teffont. 
6 . Cyclas major. —The Greater Cyclas, pi. LXXXVI. 
fig. 7. 
C. Major . Sowerby, Geo. Tr. 2 d Ser. IV. pi. 21 , fig. 13. 
Sub-rotund; rather convex; beaks nearly central, and 
produced; one side rounded, the other a little narrow, with 
a slight angle ; basal lino undulous ; surface smooth. 
The Weald, Kent, Pulborough, Henhurst, &c. 
7. Cyclas gibbosa. The Gibbous Cyclas, pi. LXXXVI. 
figs. 8 , 9. 
C. gibbosa. Sowerby, Goo. Tr. 2 d Ser. IV. pi. 21 , fig. 11 . 
Slightly ovate transversely; beaks nearly central, large, 
and produced; a concavo space under them; anterior side 
rounded; posterior side narrowed, a little truncated, and 
acute below ; surface smooth. 
Tho Weald, Sussox, and Purbeck Beds, Whitchurch. 
8 . Cyclas parva. —The Small Cyclas, pi. LXXXVI. 
fig. 1 C. 
C. parva. Sowerby, Geo. Tr. 2 d Ser. IV. pi. 21 , fig. 7. 
Sub-orbicular, slightly oblique; posterior side a little nar¬ 
rowed below; surfaco smooth. 
The Purbeck Beds, Whitchurch, Quainton, and Chicks- 
grove. 
9. Cyclas cornea.—T ho Horny Cyclas, pi. LXXXVI. 
fig. 20 . 
C. cornea. Brown, Illust. Rec. Conch. Brit. p. 93, pi. 39, 
fig. 19. 
Sub-globose, ventricose; beaks obtuse, with extremely fine, 
concentric, nearly obsolete striae. 
Tho Pleistocene Marine Formations, Clapton, Clockthorn, 
Grays, and Stutton. 
10 . Cyclas rivicola.—T ho River Cyclas, pi. LXXXVI. 
fig. 20 . 
C. rivicola. Brown, Rec. Conch. Brit. p. 93, pi. 39, figs. 
16, 17, 18. 
Transversely ovate, gibbose; beaks central; both sides 
equally rounded; surface with strong, close, regular, concen¬ 
tric striae. 
Tho Pleistocene Fresh-water Formation, Felversham and 
Southend. 
Genus XXXV.—PISCIDIUM.— Pfeiffer. 
Shell equivalve, transverse; sides unequal, completely clos¬ 
ing ; in the right valve one, and in the left two opposite, very 
small, primary teeth; behind and before two thin lamellar 
2 x 
