But the fossils above described are only a part of the original structure of the Belemnite. When in a perfect state, the cavity seen in [Lign. 142], fig. 5, is occupied by a chambered conical shell, called the phragmocone, composed of a series of shallow concave cells, of a nacreous or pearly substance, which are pierced by a siphuncle at the margin; see [Lign. 141], fig. 2.
The parts of the Belemnite at present known consist of—
1st. The spathose osselet, or guard, having at the larger end a conical cavity, called the alveolus, as in [Lign. 141], fig. 1, and [Lign. 142], fig. 5.
2dly. A conical, chambered pearly shell, termed the phragmocone, which is situated in the alveolus (as in [Lign. 141], fig. 2).
Lign. 142. Belemnites: 1/2 nat.
| Fig. | 1.— | A front view of the supposed animal of the Belemnite, byM. D’Orbigny. b. denotes the osselet, to the base of whichthe Belemnite, a, is attached. |
| 2.— | Belemnites bipartitus; the figure below shows the form of the aperture. Neocomian Formation. France. (M. D’Orbigny.) | |
| 3.— | Belemnites Listeri (G. A. M.); from the Galt. Ringmer. | |
| 4.— | A longitudinal section of B. Listeri. | |
| 5.— | Belemnites semicaniliculatus: a longitudinal section; the figure below is the aperture of the alveolus. From the Firestone (Craie tufeau) of France. | |
| 6.— | A side view of fig. 1. |
3dly. The horny prolongation of the capsule (the outer investment of the guard), called the receptacle, as in [Lign. 143].