196 
CONCIIIFERA. 
IsOCARDIA. 
of the foot of a horse, which suggested the idea of its generic 
name. 
Found in the Upper Lias, Cheltenham, at Toddenliam, near 
Shipsou-on-Stour, and near Oxford. 
Genus XVI.—MEGALODON.— Sowerby. 
Shell bivalve, equivalvc, longitudinal, acuminated towards 
the beaks; a large bifid tooth placed upon a septum across 
the beak of the right valve, and ouo irregular and more acute 
tooth, similarly situate in the left valve ; a small pit near the 
teeth for the reception of the ligament, which is anterior, long, 
and external. 
1. Megalodon cucullatus. —The Hooded Megalodon, 
pi. 79, figs. 13, 14. 
M. cucullatus . Sowerby, VI. p. 132, pi. 56*8. 
Oblong, smooth, convex, thick, ponderous ; beaks pointed, 
incurved; a deep, acute-edged pit, for the reception of the 
anterior muscle, situate close to the thick plate on which 
the hinge-teeth are situated. 
Limestone, Bradley, near Newton Bushel, Devonshire. 
2 . Megalodon carinatus. —The Keeled Megalodon, pi. 
LXXXIII. figs. 21, 22. 
M. carinatus. Goldfuss, pi. 132, fig. 9 ; Phillips, Pal. 
Foss. p. 136, pi. 00, fig. GO*. 
Transversely elongated, oblique; sub-lobate anteriorly; 
surface diagonally carinated and elevated; beaks recurved 
over the small and rather deep lunule ; surface with oblique 
and prominent lines of growth. 
In the Devonian Rocks, Newton, and Ogwall. 
Genus XVII.—ISOCARDIA.— Lamarck. 
Shell equivalve, heart-shaped, ventricose; beaks very dis¬ 
tant, divergent, and involute ; hinge with two primary com¬ 
pressed teeth in each valve, the one next the apex inflected 
under the umbo; and with one elongated, lateral tooth, situ¬ 
ate immediately before the ligament, which is external, and 
divided into two segments at its posterior extremity, both of 
which are divergent to the point of the beak in each valvo ; 
both valves provided with two lateral, remote, muscular im¬ 
pressions, the linear impression of the mantle is entire, and 
extending from one muscular impression to the other. 
1. Isocardia minima. —The Very Small Isocardia, pi. 
LX XX. figs. 2, 3. 
/. minima. Sowerby, III. p. 171, pi. 295, fig. 1. Phillips, 
Geo. York, 1. pi. 11, fig. 40. 
Sub-deltoidal, globose; anterior side a little truncated ; 
posterior side somowhat flattened and heart-shaped. 
The Cornbrash, Scarborough and Wiltshire. 
2. Isocardia abrupta. —The Abrupt Isocardia, pi. 
LXXX. fig. 7. ♦ 
Gardlta abrupta. Sowerby, I. p. 200, pi. 89, fig 2. 
Triangular, inflated ; anterior side nearly straight; beaks 
produced near one of the angles ; surface covered with oblique 
stria', somo of which meet the longitudinal ones upon the an¬ 
terior side; the others terminate abruptly on the first trans¬ 
verse rib ; the anterior side longitudinally striated; front 
provided with five or six longitudinal ridges. 
Inferior Oolite, Swanwick, Somersetshire. 
3. Isocardia striata. —The Striated Isocardia, pi. 
LXXX. fig. 4. 
Cardita striata . Sowerby, I. p. 199, pi. 89, fig. 1. 
Nearly rectangular and quadrangular, much inflated ; beaks 
situated near to one of the anglos ; anterior side rounded ; the 
whole surface with longitudinal curvilinear strife. 
Inferior Oolite, Swanwick, Somersetshire. 
4. Isocardia tener. —The Tender Isocardia, pi. LXXIX. 
figs. 2G, 27. 
/. tener. Sowerby, III. p. 171, pi, 295, fig. 2. 
Obovate, anteriorly sub-truncated, and posteriorly rounded ; 
beaks produced ; surface smooth ; the anterior side is circum¬ 
scribed by a slight ridge, which has bent striae projecting some¬ 
what beyond it; texture of the shell thin. 
The Kelloways Rock, Kelloway and Wiltshire. 
5. Isocardia rostrata. —The Beaked Isocardia, pi. 
LXXIX. figs. 18, 19. 
I. sulcata. Sowerby, III. p. 172, pi. 295, fig. 3. 
Very ventricose, deltoidal; anterior side produced and 
acute; posterior side depressed and rounded; beaks short ; 
size of a hazel nut. 
The Inferior Oolite, Cots wold and Yorkshire. 
G. Isocardia sulcata.— The Furrowed Isocardia, pi. 
LXXIX. figs. 22, 23. 
T. sulcata. Sowerby, III. p. 172, pi. 295, fig. 4. 
Orbicular, its depth exceeding its width ; beaks remote, 
much incurved, with a heart-shaped depression beneath them ; 
surface pcarlaceous, with longitudinal, broad, numerous fur¬ 
rows. 
The London Clay, Islington and Sheppy. 
7. Isocardia concentrica. —The Concentric Isocardia, pi. 
LXXIX. figs. 28, 29. 
I. concentrica. Sowerby, V. p. 147, pi. 491, fig. 1. 
Oval, heart-shaped, transversely elongated, the depth and 
length nearly equal, and considerably loss than the width ; 
beaks projecting and incurved ; surface smooth, with numerous 
shallow, trausverse furrows, which become more distant as 
they approach the edge ; shell thin. 
The Fullers Earth, Widcombo, and Great Oolite, Bath. 
8. Isocardia similis. —The Similar Isocardia, pi. LXXX. 
fig. 12. 
I. similis. Sowerby, VI. p. 27, pi. 51G, fig. 1. 
Ventricose, transversely oblong ; middle of the disk slightly 
flattened ; anterior side small, turned a little up ; base nearly 
straight; surface with very shallow trausverse undulations. 
The Lower Greensand, Sandgato, near Margate. 
9. Isocardia Cor. —The Heart Isocardia, pi. LXXX. f. 5. 
/. cor . (?) Sowerby, A T L p. 27, pi. 51G, fig. 2. Brown, 
Illust. Recent Conch. Brit. &c. p. 86, pi. 30, fig. 9, and pi. 
30*, fig. 5. Chama cor. Montagu, p. 134. 
Heart-shaped, greatly inflated, with strong, irregular, trans¬ 
verse wrinkles, which increase in coarseness and elevation as 
they approach the base ; beaks much curved and acute. 
The Red Crag, Sutton, and the Coral Crag, Ramshot. 
10. Isocardia triangularis. —The Triangular Isocardia, 
pi. LXXX. fig. 11. 
