Ammonites. 



MOLLUSCA. 



19 



appearance of Ammonites biplicatus, figs. 8. of this plate, but 

 differs from it in tiie situation and size of its tubercles, and 

 in their being united by single ribs, which are not curved ; 

 in the volutions being less inserted ; in the ambit being 

 sulcated ; and in the marginal tubercles being opposed to eaeii 

 other in place of alternating, which character also separates it 

 from A. aiiritus, pi. VII. fig. 9. 



97. A. Stokesii Stoke's Ammonite, pi. XIV. fig. 2. 



Ammonites Stohesii. Sowerby, Min. Conch. II. p. 205, pi. 

 191; De la Beche, Geo. Manuel, p. 374; Fleming, Brit. 

 An. p. 242. , 



Lenticular, depressed ; inner edge of volutions strongly 

 defined ; crossed by numerous slightly elevated ribs, which 

 are narrow at their interior side, and gradually thicken as 

 they approach the ambit, where they have a slight curvature 

 towards the aperture, and become obsolete near the back of 

 the shell ; inner volutions half concealed ; ambit thin and 

 crcnulated ; the whole shell exhibits marks of concentric striae ; 

 aperture sagittate. 



Found by Professor Buckland in a Marl bed, in the inferior 

 Oolite series, near Bridport, Dorsetshire, and named in honour 

 of Charles Stokes, Esq. a zealous and accomplislied naturalist. 

 It also occurs in the middle of England. 



98. A.PROBOsciDEUs The Proboscis Ammonite, pi. XIV. 



fig. 3. 



Ammonites proboscideus. Sowerby, Min. Conch. IV. p. 

 4. pi. 310, fig. 4, 5 ; Fleming, Brit. An. p. 246. 



Depressed, with four or five ventricose partly concealed 

 volutions ; outer one provided with two rows of large, remote, 

 blunted, almost cylindrical tubercles ; the inner series con- 

 tinuing along the exposed portion of the central volutions, 

 and marking their line of separation ; ambit concave, with 

 the outer series of large tubercles on both its edges ; aperture 

 orbicular, its width being about a third of the diameter of the 

 shell. 



Sowerby mentions two varieties of this species. 



1. With the tubercles connected by very irregular and 

 short ribs. 



2. Destitute of ribs. 



This species is distinguished from the A. tulerculatus, fig. 

 1. of this plate, by having only eight tubercles on each volu- 

 tion, in place of twelve, which marks that species ; it has also 

 a broader and ill defined back, with a very large siphuncle. 



Found in the Marl, under the Chalk at Folkstone, Cam- 

 bridge, and other places. 



99- A. DENTATUs. — The Toothed Ammonite, pi. XIV. 

 fig. 4. 



Ammonites dentattts. Sowerby, Min. Conch. IV. p. 3. pi. 

 308; Fleming, Brit. An. p. 244. A. serratus ; Parkinson, 

 Geolo. Trans. V. p. 57. 



Discoidal, umbilicated ; with numerous, prominent, slightlj' 

 curved ribs, furcated near their origin, and terminating upon 

 the margin of the ambit, where they are a little thickened 

 and bent forward ; jirodiicing on each side of the back a 

 serrated margin, with a plain, flat, intermediate space ; aper- 

 ture, two-fifths of the diameter of the shell, long, and one- 

 fourth wide. 



Found in the Marie below the Chalk at Folkstone. 



100. A. HvsTRix. — The Hedgehog Ammonite, pi. XIV. 

 fig. 5. 



Ammonites Hystrix. Phillips, Geology of Yorkshire, I. p. 

 123, pi. 2, fig. 44 ; De la Beche, Geo. Manuel, p. 294. 



Discoidal, volutions moderately inflated, furnished with 



transverse elevated ribs, emanating from" the inner margin, 



which is well defined, and terminating on the ambit, where 

 they have a gentle curve forward ; each rib provided with 

 three series of tubercles, all of which appear to have been 

 elevated, subulate, and sharp pointed ; those on the inner 

 margin, a (piarter of an inch in length, and pointing back- 

 wards ; the central series are obtuse, as if worn down ; while 

 the dorsal ones, which are entire, are nearly half an inch in 

 length, and are curved forward. 



Found in the Speeton Clay at Speeton, Yorkshire. 

 Professor Phillips says, this species is "allied to Ammonites 

 Mantelli, of which it may prove to be one of the many 

 varieties which, in Sussex, lie in the gray Marie." We, how- 

 ever, cannot agree with the professor in this opinion. 



101. A. WooLGAKi — VVoolgar's Ammonite, pi. XIV. fig. 

 6,7. 



Aiiimonites Woolgari. Mantell, Geology of Sussex, p. 197, 

 pi. 21, fig. 16, and pi. 22, iig. 7 ; Fleming, Brit. An. p. 242 ; 

 De la Beche, Geo. Man. p. 372 and 383 ; Sowerby, Min. 

 Conch. VI. p. 165, pi. 587, fig. 1. 



Discoidal, depressed, carinated ; with three or four volu- 

 tions, the central ones one-third inserted ; sides of the 

 central volutions compressed, and ornamented with remote, 

 slightly curved ribs, inclining towards the aperture, termina- 

 ting on the outer margin in compressed, carinated tubercles, 

 or spinous projections ; keel acute and deeply serrated. In 

 some specimens, there are two tubercles on the outer extre- 

 mit}' of each rib, and one on the inner margin. 



Found in the Lower Chalk, near Lewes, Sussex. 



So difiierent are the central volutions of this fossil from the 

 external one, that they might easily be mistaken as belonging 

 to distinct species, if separated from each other. They are 

 considerabljr compressed, and provided with elevated, curved 

 ribs ; while the outer one is inflated, and provided with ten 

 large, conical, spinous, parallel tubercles, on each side of the 

 keel, one tooth of which is in the centre of each pair. In the 

 central volutions, every rib is furnished with a depressed 

 tubercle, placed near to, and parallel with, the carina. Within 

 this is placed a smaller tubercle, which increases considerably 

 in size with the volutions as they progress, and becomes 

 united with a third tuberculous eminence, which gradually 

 diverges from the inner edge of the volution, until it becomes 

 obsolete ; the depressed tubercles being still, however, visible. 



This species was named by Mr Mantell in honour of the 

 late Thomas Woolgar, Esq. a zealous and acute topographer 

 and naturalist. 



102. A. BIPLICATUS. — The Two Plaited Ammonite, pi. 

 XtV. fig. 8. 



Ammonites biplicatus. Mantell, Geology of Sussex, p. 91, 

 pi. 22, fig. 6 ; Fleming, Brit. An. p. 248. 



Compressed, carinated, and slightly umbilicate ; with three 

 or four volutions, the central ones two-thirds concealed ; 

 crossed by transverse, prominent, curved, bifurcated ribs, 

 which emanate from a series of oblong, tubercular promi- 

 nences, situate on the inner margin of the volutions, and 

 terminating in distinct tubercles on the outer margin ; keel 

 depressed, bordered by alternating and compressed tubercles ; 

 aperture obtusely sagittate, its length being somewhat less 

 than the diameter of the shell. 



Found in the Blue Chalk Marie. 



This species has some affinity to the Ainmoniles laulas, 



