16 
MOLLUSCA. 
Ammonites. 
Ammonites Herveyi . Sowerby, Min. Conch. II. p. 215, 
pi. 195. 
Discoidal, gibbous, umbilicate ; four volutions, the inner 
ones nearly concealed ; sides with numerous, arcuated, sharp, 
bifurcate, or trifurcate ribs, commencing within the margin 
of the umbilicus, extending to the dorsal margin, and passing 
over the ambit, unite with the ribs of the opposite side ; 
umbilicus very deep, with the sides smooth, and a little quad¬ 
rangular ; aperture semilunar, with obtuse angles ; thickness 
of the shell nearly equal to half its diameter. Greatest 
diameter five and a half inches. 
In some instances, the branches of the ribs, after having 
passed over the back, do not reunite with those immediately 
opposite; and sometimes the third branches are left free at 
their terminations. 
Discovered on the property of the Earl of Bristol, near 
Spalden, Lincolnshire; and found at Bradford, Wiltshire; 
Knowle’s Ilill, Somersetshire; in the Kelloway’s Rock, and 
Cornbrash, Yorkshire ; and in the inferior Oolite, middle and 
south of England. 
Named in honour of the Earl of Bristol. 
76. A. Biiooki.—B rooke’s Ammonite, pi. XI. fig. 12. 
Ammonites Brooki . Sowerby, Min. Conch. II. p. 203, 
pi. 190. 
Discoidal, compressed, carinated ; four or five volutions, 
the inner ones not quite half concealed ; sides with numerous 
strong, simple, arcuated ribs, and also marked by fine lines of 
growth, the sulci and ribs being of equal breadth ; keel round, 
entire, with a deep furrow on each side ; aperture oblong- 
ovate, about a third of the diameter of the shell. Greatest 
diameter about six and a half inches. 
Found in the Blue Lias of Lyme Regis, and named in honour 
of H. J. Brooke, Esq. 
77. A. v a it i cos us.—The Warted Ammonite, pi. XII. fig. 1. 
Ammonites varicosns . Sowerby, Min. Conch. V. p. 74, 
pi. 451, figs. 4, 5. 
Discoidal, compressed ; six or seven exposed volutions ; 
both sides provided with an irregular row of tubercles 
upon their inner margin, and with large semilunar, curved, 
obtuse ribs, extending from the inside of the volutions to the 
sides of the keel, which is distinct; aperture oblong, about 
one-third of the diameter of the disk. 
When young, this species is distinctly carinated ; the inner 
edges of the volutions are provided with a series of small 
tubercles, which are united to the ribs, where they are 
developed, and as they increase in size, they become large, 
broad, and obtuse, eventually extending over the keel, and 
entirely conceal it in the full grown shell. This great 
change has frequently led to their being taken for different 
species, in those separate conditions of growth, but on a 
careful examination of the inner volutions, the form of the 
young shell may frequently be traced. 
Found in the Green-sand of Blackdown. 
78. A. rhotom agen sis.—The llouen Ammonite, pi. XII. 
fig. 2. 
Ammonites rhotom a gen sis. Cuvier and Brongniart, Env. 
de Paris, p. 83, pi. 6, fig. 2; Sowerby, Min. Conch. VI. 
p. 25, pi. 515. Ammonites Sussexensis . Mantell, Geology 
of Sussex, p. 114, pi. 20. fig. 2, and pi. 21, fig. 10. 
Discoidal, thick, subumbilicate ; four subquadrangular vo¬ 
lutions, the inner ones partly inserted; sides flattish, with 
many transverse, nearly straight, strong prominent ribs, having 
three short, blunted tubercles upon the back, and two, more 
or less obtuse, on each side ; aperture oblong, and nearly 
quadrangular; septa foliaceous. Greatest diameter twelve 
inches. 
This species is nearly’ allied to Ammonites Mantelli , pi. 4, 
figs. 4 and 9, but is distinguished by r the ribs almost invaria¬ 
bly reaching across the volutions, as well as by r its flattened 
sides, its wide umbilicus, and the central row of tubercles on 
the ambit. In the adult shell, the ribs are prominent and 
somewhat angular, the ambit broad and flat, and the central 
row of tubercles nearly obsolete. 
Found at Hamsey, Sussex, in the Gray Chalk Marie, and 
in the Chalk of Wiltshire. 
78. A. subradiatus. —The Subradiated Ammonite, pi. XII. 
fig. 3. 
Ammonites subradiatus. Sowerby, Min. Conch. V. p. 23, 
pi. 421. fig. 2. 
Lenticular, umbilicate, carinate; inner volutions entirely 
concealed ; sides covered with numerous doubly curved ribs, 
obscure in the middle of the disk, but stronger on the outer 
margin, where they are furcated ; ambit rather obtuse; keel 
small and entire, but not much developed; umbilicus small; 
aperture sagittate ; thickness of the shell about a fifth of its 
diameter. 
Found betwixt Bath and Bristol, in a mass of Ironshot 
Oolite. 
79. A. Taylori. —Taylor’s Ammonite, pi. XII. fig. 4. 
Ammonites Taylori . Sowerby, Min. Conch. VI. p. 23, 
pi. 514, fig. 1. 
Discoidal, with three entirely exposed volutions,—the inner 
ones small,—the whole crossed by about twelve remote, strong, 
prominent ribs, all of them provided with a large spiniform 
tubercle on each side of the ambit, and one or two slight 
protuberances on the rounded sides of the volutions ; aperture 
somewhat transverse and nearly round, its length not quite 
one-third of the diameter of the shell. 
Discovered in a mass of indurated Clay, somewhat like 
Ironstone, in Ilappisbury Cliff. 
Named in honour of its discoverer, R. Taylor, Esq. of 
Norwich. 
80. A. iiippocosta num. —The Horse-chestnut Ammon¬ 
ite, pi. XII. fig. 5. 
Ammonites hippocastanum. Sowerby, Min. Conch. VI. 
p. 24, pi. 514, fig. 2. 
Gibbose ; thickness equal to two-thirds its diameter ; um- 
biiicated ; four convex, deeply inserted, nearly concealed 
volutions; crossed by ten or twelve distant, almost straight, 
unequal, considerably elevated ribs, each provided with 
three tubercles upon the back or ambit, and having obtuse, 
oblong, somewhat tubercular elevations on their sides ; aper¬ 
ture transverse, obovatc. 
This species may at first sight be mistaken for the Ammon¬ 
ites rhotom ayensis, but differs in the convexity of the sides of 
the volutions, in the ribs being thicker and less numerous, and 
in the tubercles being larger, as well as iir its greater compa¬ 
rative thickness. 
Discovered by H. T. De La Beehe, Esq. in the Chalk at 
Dowlands, which abounds in grains of Green-sand and Quartz, 
and is found also at Lyme Regis. 
81. A. brevispjna. —The Short-spined Ammonite, pi. XII. 
fig. 6. 
Ammonites brevispina . Sowerby, Min. Conch. VI. p. 106, 
pi. 556 ; Phillips, Geology of Yorkshire, I. p. 174. 
Discoidal, with five or six entirely exposed, compressed 
