Secondly, a conical thin horny sheath, or cup, commencing from the base of the hollow cone of the fibro-calcareous sheath, and enlarging rapidly as it extends outwards to a considerable distance. Pl. 44', Fig. 7, b, e, e', e". This horny cup formed the anterior chamber of the Belemnite, and contained the ink-bag, (c,) and some other viscera.*

Thirdly, a thin conical internal chambered shell, called the Alveolus, placed within the calcareous hollow cone above described. (Pl. 44, Fig. 17, a. and Pl. 44', Fig. 7, b, b'.)

This chambered portion of the shell is closely allied in form, and in the principles of its construction, both to the Nautilus and Orthoceratite. (See Pl. 44, Fig. 17, a, b. and Fig. 4.) It is divided by thin transverse plates into a series of narrow air-chambers, or areola, resembling a pile of watch-glasses, gradually diminishing towards the apex.

is made up of a pile of cones, placed one within another, having a common axis, and the largest enclosing all the rest. (See Pl. 44, Fig. 17.) These cones are composed of crystalline carbonate of lime, disposed in fibres that radiate from an eccentric axis to the circumference of the Belemnite. The crystalline condition of this shell seems to result from calcareous infiltrations (subsequent to interment,) into the intervals between the radiating calcareous fibres of which it was originally composed. The idea that the Belemnite was a heavy solid stony body, whilst it formed part of a living and floating sepia, would be contrary to all analogies afforded by the internal organs of living Cephalopods. The odour, resembling burnt horn, pro duced on burning this part of a Belemnite, arises from the remains. of horny membranes interposed between each successive fibro-calcareous

cone.

An argument in favour of the opinion that Belemnites were internal organs, arises from the fact of their surface being often covered with vascular impressions, derived from the mantle in which it was enclosed. In some species of Belemnites the back is granulated, like the back of the internal shell of Sepia officinalis.

* This laminated horny sheath is rarely preserved in connexion with the fibro-calcareous shelly sheath; but in the Lias at Lyme Regis, it is frequently found without the shell. Certain portions of it are often highly nacreous, whilst other parts of the same sheath retain their horny condition

The transverse plates are outwardly concave, inwardly convex; and are perforated by a continuous siphuncle, (Pl. 44, Fig. 17, b.,) placed on the inferior, or ventral margin.

We have already (Ch. XV. Section II.) described the horny pens and ink-bags of the Loligo, found in the Lias at Lyme Regis. Similar ink-bags have recently been found in connexion with Belemnites in the same Lias. Some of these ink-bags are nearly a foot in length, and show that the Belemno-sepiæ, from which they were derived, attained great size.

*

* In 1829, I communicated to the Geological Society of London a notice respecting the probable connexion of Belemnites with certain fossil inkbags, surrounded by brilliant nacre, found in the Lias at Lyme Regis. (See Phil. Mag. N. S. 1829, p. 388.) At the same time I caused to be prepared the drawings of fossils, engraved in Pl. 44", which induced me to consider these ink-bags as derived from Cephalopods connected with Belemnites. I then withheld their publication, in the hope of discovering certain demonstration, in some specimen that should present these ink-bags in connexion with the sheath or body of a Belemnite, and this demonstration has at length been furnished by a discovery made by Professor Agassiz (October, 1834,) in the cabinet of Miss Philpotts, at Lyme Regis, of two im. portant specimens which appear to be decisive of the question. (See Pl. 44', Figs. 7, 9.)

Each of these specimens contains an ink-bag within the anterior portion of the sheath of a perfect Belemnite; and we are henceforth enabled with certainty to refer all species of Belemnites to a family in the class of Cephalopods, for which I would, in concurrence with M. Agassiz propose the name of Belemno-sepia. Such ink-bags are occasionally found in contact with traces of isolated alveoli of Belemnites: they are more frequently surrounded only by a thin plate of brilliant nacre.

The specimen (Pl. 44′′, Fig. 1,) was procured by me from Miss Mary Anning in 1829, who considered it as appertaining to a Belemnite. Near its lower end we see the lines of growth of the horny anterior sheath, but no traces of the posterior calcareous sheath; within this horny sheath is placed the ink-bag. The conical form of this anterior chamber seems to have been altered by pressure. It is composed of a thin laminated substance (see Pl. 44", Fig. 1, d.,) which in some parts is brilliantly nacreous, whilst in other parts it presents simply the appearance of horn. The outer surface of this cup is marked transversely with gentle undulations, which probably indicate stages of growth. Miss Baker has a Belem

The fact of these animals having been provided with so large a reservoir of ink, affords an à priori probability that they had no external shell; the ink-bag, as far as we yet know, being a provision confined to naked Cephalopods, which have not that protection from an external shell, which is afforded by the shell of the N. Pompilius to its inhabitant, that has no ink-bag. No ink, or ink-bags have been ever seen within the shell of any fossil Nautilus or Ammonite: had such a substance existed in the body of the animals that occupied their outer chamber, some traces of it must have remained in those beds of lias at Lyme Regis, which are loaded with Nautili and Ammonites, and have preserved the ink of naked Cephalopods in so perfect a condition. The young Sepia officinalis, whilst included within the transparent egg, exhibits its ink-bag distended with ink, provided beforehand for use as soon as it is excluded; and this ink-bag is surrounded by a covering of brilliant nacre

nite from the inferior Oolite near Northampton, in which one half of the fibrous cup being removed, the structure of the conical shell of the alveolus is seen impressed on a cast of iron-stone, and exhibits undulating lines of growth, like those on the exterior of the shell of N. Pompilius.

M. Blainville, although he had not seen a specimen of Belemnite in which the anterior horny conical chamber is preserved, has argued from the analogy of other cognate chambered shells that such an appendage was appertinent to this shell. The soundness of his reasoning is confirmed by the discovery of the specimen before us, containing this part in the form and place which he had predicted. "Par analogie elle était donc évidemment dorsale et terminale, et lorsqu'elle était complète c'est-à-dire pourvue d'une cavité, l'extremité postérieure des viscères de l'animal (très-probablement l'organe sécréteur de la génération et partie du foie) y était renfermée.”Blainville Mém. sur les Bèlemnites. 1827. Page 28.

Count Munster (Mem. Geol. par. A. Boue, 1832, V. 1, Pl. 4, Figs. 1, 2, 3, 15,) has published figures of very perfect Belemnites from Solenhofen, in some of which the interior horny sheath is preserved, to a distance equal to the length of the solid calcareous portion of the Belemnite (Pl. 44', Figs. 10, 11, 12, 13,) but in neither of these are there any traces of an ink-bag.

ous matter, similar to that we find on certain internal mem branes of many fishes.*

• I would here add a few words of explanation of the curious fact, that among the innumerable specimens of Belemnites which have so long attracted the attention of naturalists, not one has till now been found entire in all its parts, having the ink within its external chamber; either the fibrocalcareous sheath is found detached from the horny sheath and ink-bag, or the ink-bag is found apart from the Belemnite, and surrounded only by the nacreous horny membrane of its anterior chamber. We know from the condition of the compressed nacreous Ammonites in the Lias-shale at Watchet, that the nacreous lining only of these shells is here preserved, whilst the shell itself has perished. This fact seems to explain the absence of the calcareous sheath and shell in almost every specimen of ink-bags at Lyme Regis, which is surrounded with iridescent nacre, like that of the Ammonites of Watchet. The matrix in these cases may have had a capacity for preserving nacreous or horny substances, whilst it allowed the more soluble calcareous matter of shells to be removed, probably dissolved in some acid.

The greater difficulty is to explain the reason, why amidst the millionsof Belemnites that are dispersed indiscriminately through almost all strata of the Secondary series, and sometimes form entire pavements in beds of shale connected with the Lias and Inferior oolite, it so rarely happens that either the horny-sheath, or the ink-bag, have been preserved. We may, I think, explain the absence of the nacreous horny-sheath, by supposing that a condition of the matrix favourable to the preservation of the calcareous sheath was unfavourable to the preservation of horny membrane; and we may also explain the absence of ink-bags, by supposing that the decomposition of the soft parts of the animal usually caused the ink to be dispersed, before the body was buried in the earthy sediment then going on.

At the base of Golden Cap hill, near Charmouth, the shore presents two strata of marl almost paved with Belemnites, and separated by about three feet only of comparatively barren marl. As great numbers of these Belemnites have Surpulæ, and other extraneous shells attached to them, we learn from this circumstance that the bodies and ink-bags had decomposed, and the Belemnites lain some time uncovered at the bottom. These facts are explained by supposing that the sea near this spot was much frequented by Belemno-sepiæ during the intervals of the deposition of the Lias. Similar conclusions follow, from the state of many Belemnites in the chalk of Antrim, which had been perforated by small boring animals, whilst they lay at the bottom of the sea, and these perforations filled with casts of chalk

Comparing the shell of Belemnite, with that of Nautilus, we find the agreement of all their most important parts to be nearly complete ;* and the same analogies might be traced through the other genera of chambered shells.†

or flint, when the matter of the chalk strata was deposited upon them, in a soft and fluid state. (See Allan's Paper on Belemnite, Trans. Royal Soc. Edin., and Miller's Paper, Geol. Trans. Lond. 1826, p. 53.)

Thus of the millions of Belemnites which crowd the Secondary formations, only the fibro-calcareous sheath and chambered alveoli are usually preserved; whilst in certain shale beds this sheath and shell have sometimes entirely disappeared, and the horny or nacreous sheath or ink-bag alone remain. See Pl. 44", Fig. 1, 2, 3. 4, 5, 6, 7, 8. In the rare case, Pl. 44', Fig. 7, which has afforded the clue to this hitherto unexplained enigma, we have all the three essential parts of a Belemnite preserved in their respective places nearly entire. The ink-bag (c) is placed within the anterior horny cup (e, e', e';) and the chambered alveolus, (b b') within the hollow cone of the posterior fibro-calcareous shell, or common Belemnite,

* The air-chambers and siphuncle are, in both these families, essentially the satne.

In Belemnites, the anterior extremity of the fibro-calcareous shell, which forms a hollow straight cone, surrounding the transverse plates of the chambered alveolus, represents the hollow coiled up cone containing all the transverse plates, which make up the alveolus of the Nautilus.

The anterior horny cup, or outer chamber of the Belemnite, surrounding the ink-bag, and other viscera, represents the large anterior shelly chamber which contains the body of the Nautilus.

The posterior portion of the Belemnite, which is elongated backwards into a fibrous pointed shaft, is a modification of the apex of the straight cone of this shell, to which there seems to be no equivalent in the apex of the coiled-up cone of Nautilus. The cause of this peculiar addition to the ordinary parts of shells, seems to rest in the peculiar uses of the shaft of the Belemnite, as an internal shell, acting like the internal shell of the Sepia Officinalis, to support the soft parts of the animals, within the bodies of which they were respectively enclosed. The fibrous structure of this shaft is such as is common to many shells, and is most obvious in the Pinnæ.

+ Comparing the Belemnite, or internal shell of Balemno-sepia with the Sepiostaire, (Blainville,) or internal shell of the Sepia Officinalis, we have the following analogies. In the Sepiostaire, (Pl. 44′, Fig. 2, a. e. and Figs. 4, 4, 5,) the small conical apex (a) represents the apex of the long calcareous posterior sheath of the Belemnite, (Fig. 7, a.,) and the