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Figs.

PLATE 37. V. I. p. 258. Note.

1. Ammonites Amaltheus

Gibbosus

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(Schlotheim). Gloucester. Lias.

2. A. Varicosus (Sowerby) Black Down, Devon. Green Sand.

3. A Humphriesianus (Sowerby) . . Sherborne

6. A. Bucklandi

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Inferior Oolite.

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7. A. Lautus

8. A. Catena

9. A. Varians

10. A. Striatus . .

(Zieten)
(Reinicke)

a. Exterior dorsal margin.

b. Back view of the shell.

c. Transverse section of shell.

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The figures in this Plate are selected to exemplify some of the various manners in which the shells of Ammonites are adorned and strengthened by ribs, and flutings, and bosses. In Vol. I. p. 257, instances are mentioned of similar contrivances which are applied in Art to strengthen thin plates of metal. Workers in Glass have also adopted a similar expedient in their method of fortifying small wine flasks of thin glass, made flat, and portable in the pocket, with a series of spiral flutings passing obliquely across the sides of the flask, as in many of the flattened forms of Ammonite. Similar spiral flutings are introduced for the same purpose on the surface of thin glass pocket smellingbottles. In other glass flasks of the same kind which are made in Germany, the addition of bosses to the surfaces of the flat sides of the bottles, produces a similar double result of ornament and strength.

PLATE 38. V. I. p. 262. Note.

Air-chambers of Ammonites heterophyllus, filled with Lias, and showing in a remarkable degree the effect of the undulating course of the edges of the transverse plates beneath the flat sides of the outer shell.

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A portion of the outer shell is preserved at c. and impressions of the fluted interior of the shell, which has fallen off, are visible at d. (Original.)

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This Plate presents a longitudinal view of the same fossil, of which a side view is given in the last figure. The same transverse plates that approximate so closely beneath the sides of the shell, where it is flat and feeble, (Pl. 38.) are distant from each other along the dorsal portion, which from its convex form is strong.

The Siphuncle is preserved in its proper dorsal place at d. The elevations and depressions of the transverse plate in front of this figure exemplify the theory of Von Buch, respecting the use of the Lobes and Saddles formed by the undulations of its outer margin. See V. I. p. 267, and Note. (Original.)

PLATE 40. V. I. p. 272. Note.

Fig. 1. Ammonites Henslowi (Goniatites,) from Transition limestone in the Isle of Man.

The Lobes are simple, and without foliations; their form resembles that of the slipper-shaped lobe of the Nautilus Ziczac, and Nautilus Sypho. See Pl. 43.

The lobes D. L. 1. V. are pointed inwards, and the intermediate Saddles S. d. S. L. S. V. are rounded outwards; according to the type of Ammonites. (Original.)

Fig. 2. Ammonites striatus (Goniatites,) from the Coal Shale of Lough Allen in Connaught, having its lobes and saddles disposed in the same directions as in Fig. 3, the delicate longitudinal stria and

transverse ribs of the outer shell are strengthened by repeated intersections of the subjacent edges of the transverse Plates. (Original.)

Fig. 3. Back view of Ammonites sphæricus, from the limestone of Derbyshire, showing the position of the siphuncle upon the dorsal margin, with its collar advancing outwards between the two simple dorsal lobes; the lateral lobes are also simple and without foliations, and pointed inwards. (Martin Pet. Der. T. 7.)

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Fig. 4. Ammonites nodosus (Ceratites). This is one of the species peculiar to the Muschel-kalk. The descending lobes terminate in a few small denticulations, pointed inwards, and the ascending saddles are rounded outwards, after the normal character of Ammonites. (Zeiten. Tab. II. Fig. 1. a.). Fig. 5. Back of A. Nodosus, showing the dorsal lobes pointed inwards, and the collar around the siphuncle advancing outwards. No edges of the transverse plates are placed beneath the dome-shaped Tubercles; these derive sufficient strength from their vaulted form. (Zeiten. Tab. II. Fig. 1. b.)

PLATE 41. V. I. p. 264.

Ammonites giganteus, found in the Portland stone at Tisbury in Wiltshire. This beautiful fossil is in the collection of Miss Benett. The chambers are all void, and the transverse Plates and Shell converted to Calcedony. (Original.)

PLATE 42. V. I. pp. 264, 265. Note.

Fig. 1. Cast of a single chamber of Nautilus hexagonus, showing the simple curvatures of the edges of the transverse plates, and the place of the Siphuncle. (Original.)

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Fig. 2. Cast of a chamber of Ammonites excavatus, having a complex form derived from the denticulated edges of the transverse plates. See V. I. pp. 264, 265, Note. (Original.)

Fig. 3. Casts of three chambers of Ammonites catena, with the Membrane of the Siphuncle on its dorsal margin. See V. I. p. 264, Note, and p. 265, Note.

The course of the transverse plates is beneath the depressed and weakest parts of the external shell, avoiding the bosses at c, d, e, which from their form are strong. (Original.)

Fig. 4. Ammonites varicosus, from the Green Sand of Earl Stoke, Wilts. Nat. size. See V. I. p. 265, Note. (Original.)

Figs. 5. 6. Portions of the same shell, having the transverse Plates and Siphuncle converted to Calcedony. See V. I. pp. 265 and 266, Note. (Original.) Fig. 7. Ammonites varicostatus, (nobis,) an undescribed species of Ammonite from the Oxford Clay at Hawnes, 4 m. S. of Bedford. Diameter 9 inches.

The name Varicostatus expresses the remarkable change in the character of the Ribs, near the outer termination of the air chambers.

On the inner whorls of the shell, these ribs are narrow, and highly raised, set close to one another, and bifurcated at the back of the shell, (from d. to c.); but near the outer chamber (b. to a.) they become broad and distant, and the dorsal bifurcation

ceases.

The edges of the transverse plates are exposed by the removal of the shell from c. to b., they appear also at a. d. (Original.)

Similar variations in the form of the ribs occur in Ammonites biplicatus and Ammonites decipiens.

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PLATE 43. V. I. pp. 270, 271.

Fig. 1. Fragment of Nautilus sypho, in the collection of W. I. Broderip, Esq. from the Miocene division of the Tertiary formations at Dax, near Bourdeaux. The accidental fractures of this fossil afford an instructive display of the disposition of the transverse Plates and Siphuncle. (Original.)

Fig. 2. Another fractured shell of the same species from Dax, in the collection of Mrs. Buckland, showing at

a, a', as, the disposition of the lateral lobes. See V. I. p. 271, Note. (Original.)

Fig. 3. Cast of the interior of Nautilus Ziczac, in the collection of Mr. James Sowerby, showing the disposition of the lateral lobes. (See V. I. pp. 271, 272. (Original.)

Fig. 4. Cast of a single chamber of Nautilus Ziczac, in

the collection of Mr. J. Sowerby, showing the disposition of the ventral and dorsal Lobes and Siphuncle. See V. I. p. 271, Note. (Original.)

PLATE 44. V. I. p. 273, et seq.

Fig. 1. Molluscous animal inclosing the Spirula Peronii. See V. I. p. 273.* (Blainville.)

Fig. 2. Section of a Spirula (Nat. size), showing its transverse Plates and siphuncular sheath. (Original.)

* M. Robert has recently discovered between the Canaries and Cape Blanc, several imperfect bodies of a small species of molluscous animal, each inclosing a Spirula.

In all these the position of the shell is not at the posterior extremity, as in the figure of the specimen found by Peron, but in the back, parallel to the axis of the body, like the shell of the Sepiostaire, or internal shell of the common Sepia. This position agrees with that of the animal figured by Blainville, if we suppose the caudal portion of the latter to have been lost.

On each side of the body are two expansions that act like Fins, as in the Sepiole. Beneath the neck is the aperture of the Funnel. In

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