8 



MOLLUSCA. 



Ammonites. 



carbonate of iron tliat has lined its chambers, is truly 

 beautiful." 



Our figure, pi. IV. fig. 8, is a representation of a longi- 

 tudinal section of this species, to shew the internal structure 

 of the shell, and particularly to exhibit the situation of the 

 siphuncle, (preserved in a carbonaceous state,) which is seen 

 passing along the whole dorsal margin, to the commencement 

 of the outer chamber. The body of the animal occupied the 

 space from a to b. The letters c, d, e,f, g, h, point out the 

 situation of the siphuncle, which is always placed upon the 

 exterior, or dorsal margin. It is represented in black, and 

 passes from the external chamber i to the inner extremity of 

 the volutions. 



22. A. NuTFiELDENSis. — The Nutfield Ammonite, pi. VI. 

 fig. 5. 



Sowerby, Min. Conch. II. p. 11, ph 108. 



Involute, with four or five volutions, much concealed ; 

 crossed by numerous, strong, prominent ribs, with interme- 

 diate shorter ones, which are more than three-fourths towards 

 the internal side of the volutions ; these are frequently arranged 

 in pairs, but the whole pass over the rounded ambit, or back ; 

 the larger ones being most prominent in the centre ; septa 

 rather numerous, lobed and sinuated in the ordinary manner ; 

 aperture subcordiforni, two-fifths of the diameter in length, 

 nearly the same in width, and rounded behind. Diameter 

 from three inches to one foot. 



This species is found abundantly in the Green Sandstone 

 at Hythe and other places, which rests above the thickest 

 beds of Fuller's Earth. Most of the specimens are casts in 

 dark iron clay, and their external hue generallj' ochreous. 



23. A. TRiPLiCATUs The Thi-ee-Pleated Ammonite, pi. 



VI. fig. 6. 



Sowerby, Min. Conch. I. p. 208, pi. 92, fig. 2. 



Involute, with four volutions, the inner ones exposed ; 

 surface covered with doubly curved, alternating, long and 

 short ribs ; between every two long ones are three siiort, 

 which reach a little beyond the centre of the volutions ; 

 septa distant ; aperture obovate, about half the diameter in 

 length, and its width one-third. 



In some instances there are only two intermediate ribs 

 between the longer ones. 



Discovered at Portland Island by Mr Bryer of Weymouth, 



24. A. EXCAVATUS — The Hollow Ammonite, pi. VI. fig. 7- 

 Sowerby, Min. Conch. 11. p. 5, pi. 105. 



Involute, lenticular, subunibilicate, with a sharp, crenulated 

 carina ; on each side of which a slightly concave groove inter- 

 venes between it and the sides of the shell, which ai-e uniformly 

 convex ; volutions about six, entirely exposed in the young 

 state, and the whole divided by a flattened groove, forming 

 a rectangular margin along the interior sides of the volutions ; 

 the entire shell covered with obscure curved ribs, which are 

 stronger in the inner volutions and in young shells ; aperture 

 sagittate, extending to about half the diameter of the shell ; 

 and its width at back being about a third. Greatest diameter 

 four inches. 



First discovered at Sliotover, near Oxford, by Mr Sowerby. 



25. A. jUGOsus — The Ilidged Ammonite, pi. VI. fig. 8. 

 Sowerby, Min. Conch, p. 207, pi. 92, fig. 1. 



Involute, with a small, distinct, sharp carina ; four volu- 

 tions half concealed ; covered with large, obtuse, straight ribs, 

 very regular, equal to the space between them, and becoming 

 obsolete behind ; septa not numerous, their margins slightly 



plaited ; aperture ovate, narrower behind, and occupying 

 about two-fifths the diameter of the shell, and its width one- 

 fifth ; shell delicate and very thin. 



Discovered by Mr Strangeways, in Limestone, at White 

 Lackington Park, near Ilminster. 



26. A. COMMUNIS The Common Ammonite, pi. VI. fig. 9. 



Sowerby, Min. Conch. II. p. 10. fig- 2, 3 ; Corne d'Ammon 



a raies doublees ver le haut du dos. Bourguet, pi. 42. 

 fig. 276. 



Involule, with six or eight rounded, wholly exposed 

 volutions ; crossed by numerous strong, prominent, straight 

 ribs, which become furcated towards the dorsal margin, 

 and are sometimes reunited on the ambit, and again divided 

 on the opposite side of the shell ; aperture three-fourths of 

 a circle, and occupying about one-fifth the diameter of the 

 shell ; septum round. 



This species is very common in the Alum Clay at Whitby ; 

 it is generally dark bluish-black, or brownish black, with a 

 metallic lustre produced by pyrites. 



A superstitious belief prevails at Whitbj', and all over the 

 neighbouring country, that these Ammonites are petrified 

 snakes which infested the precincts of the monastery of 

 Whitby ; and these were not only turned to stone, but also 

 beheaded, by a prayer from the abbess St Hilda. Indeed, 

 tills miracle is much insisted upon by all ancient writers who 

 have occasion to mention either Whitby or St Hilda. It is 

 thus alluded to by Sir Walter Scott, in Marmion ; the nuns 

 are said to tell, 



And how, of thousand snakes, each one 

 Was changed into a coil of stone, 



When holy Hilda pray'd ; 

 Themselves, within their holy bound, 

 Their stony folds had often found. 



Tlie Convent, Stanza 13. 



There arc individuals in Whitby who sell this Ammonite, 

 and not unfreqiiently form a head upon the outer volution, 

 in imitation of that of a snake, and impose upon those who 

 are unacquainted with their being the remains of testaceous 

 shells. 



27. A. ANGULATUS The Angulated Ammonite, pi. VI. 



fig. 10. 



Sowerby, Min. Conch. II. p. 9. pi. 107. fig. 1. 



Involute, with seven or eight well rounded and wholly 

 exposed volutions, which are angular along their inner sides, 

 and divided by a narrow, concave, flattened space, from 

 whence proceed numerous prominent ribs, wliich are furcated 

 as they pass over the back or ambit, — whicli is slightly flat- 

 tened ; aperture somewhat longer than wide, the width being 

 equal to about one-fifth the diameter of the shell ; the sinu- 

 ated margins of the septa are rather close, and considerably 

 more so than in the A. communis. 



Discovered by .1. M. Sowerby, Esq. in the White alum 

 clay at Whitby, and has much the appearance of ^. comnmnis, 

 but is at once distinguished from that species by the groove 

 which separates the volutions. 



28. A. BucKLANDi — Huckland's Ammonite, pi. VII. fig. 

 1 and 2. 



Sowerby, Mill. Conch. II. p. 69, pi. 130. Buckland's Geo- 

 logy and Mineralogy Considered, II. p. 59, pi. 37, fig. 6. 



Depressed, consisting of five volutions, the inner ones 

 entirely exposed, furnished with large obtuse ribs, which 

 become more produced as tliey approach the back, round 



