[066]

Illustrations of the probable nature of the Animals that gave origin to Belemnites.*

In the descriptions of Pl. 44'. and Pl. 44". the following letters indicate the same parts in each specimen to which they are applied.
a. The Apex of the calcareous shell, or sheath.
b. Alveolar portion, or chambered shell.
c. Ink-bag.
d. and e. Portions of the thin anterior horny sheath, sometimes highly nacreous.
f. Neck of Ink-bag

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Fig. l. Imaginary restoration of Belemnosepia, shewing the probable place of its Ink-bag, and of the internal shell or Belemnite. The three component parts of this Belemnite are represented as if longitudinally bisected: the place assigned to this Ink-bag is nearly the same as in the recent Loligo. (Original.)

Fig. 2. Sepia officinalis, shewing the position of the internal shell or sheath (Sepiostaire) within the dorsal portion of its sac. Its apex (a,) and cal careous dorsal plates (e,) correspond with the apex calcareous conical sheath of a Belemnite.

Fig. 3. Sepia officinalis, laid open along the ventral portion of its Sac, to shew the position of its Ink- bag. (Original.)

Figs. 3. a. 3. b. 3. c. Rhyncholites, found in contact with Belemnites in the Lias at Lyme Regis. Nat. size. (Original.)

Fig. 3. d. Beak of a small Testudo from Chalk, in the collection of Mr. Mantell, shewing a fibro-cancellated bony structure, very different from the compact shelly condition of the Rhyncholite, for which it may from its size and shape be mistaken. (Original.)

Fig. 4. Ventral surface of a Sepiostaire; the elongated shallow cone, or cup, (e. e. e'. e'.) is composed of very thin calcareous plates, alternating with horny membranes, which are expanded outwards to form the thin margin of the cone. This irregular cone or shell represents the hollow cone at the larger extremity of the Belemnite, (Fig. 7. b. b'.e. e'. e".) which includes its Alveolus (b. b'.) and Ink-bag (c.). Within this shallow sub-conical shell of the Sepiostaire is contained its alveolus, or calcareous chambered portion, (Fig. 4. b.) which represents the  [068] chambered alveolus in the Belemnite, (Fig. 7. b. b'.) but has no Siphon. (Blainville.)

Fig. 4'. Longitudinal section of the apex of the shell of Sepia officinalis. This apex is composed of granular calcareous matter (a.), alternating with conical horny laminæ, which expand laterally into the horny margin (e.). (Original.)

Fig. 5. Longitudinal view of Fig. 4. The apex (a.) represents the apex of a Belemnite. The back of the shell (e.) the dorsal part of a Belemnite; and the alveolar portion (b. b'.) represents the internal chambered shell of a Belemnite. (Blainville.)

Fig. 6. Anterior extremity of the lamellæ, or alveolar
plates, exposed by a longitudinal section in Fig. 5.
In the mature animal these lamellæ are nearly 100
in number; a few of them only are here represented.

These alveolar plates form the internal chambers of the Sepiostaire, and represent the transverse plates of the Alveolus in Belemnites, and other chambered shells; but as the Sepiostaire has no siphuncle, its chambers seem not subservient, like those of the Belemnite, to the purpose of varying the specific gravity of the animal; the intervals be tween its plates are occupied by an infinite number of thin winding partitions standing perpendicularly between the lamellæ.

Figs. 6'. 6". Thin calcareous partitions winding between, and supporting the alveolar plates of the Sepiostaire The sinuous disposition of these partitions increases their efficacy in resisting pressure, on the same principle, as in the foliated edges of the transverse plates of Ammonites.* The sinuosity of the

* Dr. Fleming has accurately described the structure of these partitions, as exhibiting perpendicular laminæ, waved and folded in brain-like gyrations which occasionally anastomose.
 

[069] calcareous partitions is least near the margin of the lamellæ. See Fig. 6'. (Original.)

Fig. 6'''. Columnar appearance of the sinuous partitions when viewed laterally. (Original.)

Fig. 7. Unique specimen of Belemnites ovalis, from the Lias at Lyme Regis, in the collection of Miss Philpotts. A fracture at b'. shews the chambered areolæ of the Alveolus. At e. the thin conical anterior horny sheath originates in the edge of the calcareous sheath, and extends to e". The surface of this anterior sheath exhibits wavy transverse lines of growth; it is much decomposed, slightly nacreous, and flattened by pressure.

Within this anterior conical sheath the Ink-bag is seen at c. somewhat decomposed, and partially altered to a dark grey colour. (Original.)

Fig. 8. Portion of the Ink-bag broken off from Fig. 7. c. and covered by that portion of the horny case which lay above it. The transverse lines, e. on this portion, are the continuation of the lines of growth on the horny sheath of Fig. 7. e. e'. e". (Original.)

Fig. 9. Belemnites Pistilliformis? from the bias at Lyme, in the collection of Miss Philpotts, having a portion of its ink-bag at c. (Original.)

Fig. 10. 11. 12. Belemnites from the Jura limestone of Solenhofen, figured by Count Munster in Boué's Mémoires Géologiques, Vol. l. Pl. 4. In 10 and 12 the form of the anterior horny sheath is preserved, to a length equal to that of the calcareous shaft of the Belemnite, but in none of them is the Ink-bag visible.* (Munster.) [070]

* Von Meyer mentions (Palæologica, P. 322, 1st Edit. 1832,) that he has seen an Ink-bag at the upper end of a Belemnite from the Lias of Banz, and asks, " Do Belemnites possess an Ink-bag like that of the Sepia?"

Fig. 13. Chambered alveolar cone and horny sheath of a large Belemnite from the limestone of Solenhofen; the calcareous sheath or Belemnite itself has disappeared. (Munster.)

Fig. 14. Belemnites brevis? from the Lias at Lyme; Nat. size. The length of the shaft of this Belemnite does not exceed that of the Beloptera (Fig. 15); a small fragment only of its alveolus is preserved, but the place it occupied is filled with calcareous spar, and the hollow cone above it with lias. (Original.)

Fig. 15. Beloptera. In this fossil we have an intermediate link between the Belemnite and the shell or sheath of Sepia officinalis. a. represents the apex of the sheath, e. e. its posterior expansion, analogous to that at Fig. 4. e. e. and at Fig. 4'. e.; e' is its anterior expansion, bearing on its internal surface annular marks derived from the transverse septa of the alveolus. (Blainville.)