16 



MOLLUSCA. 



Ammonites. 



Ammonites Herveyi. Sowerby, Min. Conch. II. p. 215, 

 pi. 195. 



Discoidal, gibbous, umbilicate ; four volutions, the inner 

 ones nearly concealed ; sides witli 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 tlie 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 Hill, 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. Brooki. — Brooke's Ammonite, pi. XI. fig. 12. 

 Ammonites Brooki. Sowerby, Min. Conch. II. p. 20.3, 



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. vARicosus. — The Warted Ammonite, pi. XII. fig. 1. 

 Ammonites varicosus. 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. RHOTOMAGENSis. — The Rouen Ammonite, pi. XII. 

 fig. 2. 



Ammonites rJwtomagensis. Cuvier and Brongniart, Env. 

 de Paris, p. 83, pi. 6, fig. 2 ; Sowerby, Min. Conch. VL 

 p. 25, pi. 515. Ammonites Sussexetisis. Mantell, Geology 

 of Sussex, p. 114, pi. 2U. fig. 2, and pi. 21, fig. 10. 



Discoidal, thick, subumljilicatc ; four subqiiadrangular 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 the ribs almost invaria- 

 bly reaching across the volutions, as well as by 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, 



ph 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 Happisbury Cliff. 



Named in honour of its discoverer, R. Taylor, Esq. of 

 Norwich. 



80. A. iiippocosTANUM. — 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- 

 bilicated ; 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, obovate. 



This species may at first sight be mistaken for the Ammon- 

 ites rhotomagensis, 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 in its greater compa- 

 rative thickness. 



Discovered by H. T. De La Beche, Esq. in the Chalk at 

 Dowlands, which abounds in grains of Green-sand and Quartz, 

 and is found also at Lyme Regis. 



81. A. BREvispiNA The Short-spined Ammonite, pi. XII, 



fig. 6. 



Ammonites brevispina. Sowerby, Min. Conch. VI. p. 106, 

 pi. 55(5 ; Phillips, Geology of Yorkshire, I. p. 174. 



Discoidal, with five or six entirely exposed, compressed 



