bered shells, called Lituites. (Pl. 44, Fig. 3.) These are partially coiled up into a spiral form at their smaller extremity, whilst their larger end is continued into a straight tube, of considerable length, separated by transverse plates, concave outwards, and perforated by a siphuncle (a.) As these Lituites closely resemble the shell of the recent Spirula (Pl. 44, Fig. 2,) their office may have been the same, in the economy of some extinct Cephalopod.

Baculite.

As in rocks of the Transition series, the form of a straight Nautilus is presented by the genus Orthoceratite, so we find in the Cretaceous formation alone, the remains of a genus which may be considered as a straight Ammonite. (See Pl. 44, Fig. 5.)

The baculite (so called from its resemblance to a straight staff) is a conical elongated, and symmetrical shell, depressed laterally, and divided into numerous chambers by transverse plates, like those in the Ammonite, are sinuous, and terminated by foliated dentations at their junction with the external shell; being thus separated into dorsal, ventral, and lateral lobes and saddles, analogous to those of Ammonites.*

It is curious, that this straight modification of the form of Ammonites should not have appeared, until this Family had arrived at the last stage of the Secondary deposites, throughout which it had occupied so large an extent; and that, after a comparatively short duration, the Baculite

* The external chamber (a) is larger than the rest, and swelling; and capable of containing a considerable portion of the animal. The outer shell was thin, and strengthened, like the Ammonite, by oblique ribs. Near the posterior margin of the shell, the transverse plates are pierced by a Siphuncle (Pl. 44, 5, c.) This position of the Siphuncle, and the sinuous form and denticulated edges of the transverse plates, are characters which the Baculite possesses in common with the Ammonite.

should have become extinct, simultaneously with the last of the Ammonites, at the termination of the Chalk formation.

Hamite.

If we imagine a Baculite to be bent round near its centre, until the smaller extremity became nearly parallel to its larger end, it would present the most simple form of that cognate genus of chambered shells, which, from their frequently assuming this hooked form, have been called Hamites. At Pl. 44, Fig. 9, 11, represent portions of Hamites which have this most simple curvature; other species of this genus have a more tortuous form, and are either closely coiled up, like the small extremity of a Spirula, (Pl. 44, Fig. 2,) or disposed in a more open spiral. (Pl. 44, Fig. 8.*)

It is probable that some of these Hamites were partly internal, and partly external shells; where the spines are present, the portion so armed was probably external. Nine species of Hamites occur in the single formation of Gault or Speeton clay immediately below the chalk, near Scar

Both these forms of Hamite bear the same relation to Ammonites that Lituites bear to Nautili; each being nearly such as shells of these genera would respectively present, if partially unrolled. See Phillips' Geol. Yorkshire, Pl. 1, Figs. 22, 29, 30.

Baculites and Hamites have two characters which connect them with Ammonites; first, the position of the Siphuncle, on the back, or outer margin of the shell, (Pl. 14, Figs. 5b, c. 8a, a. 10, 11, a. 12, a. 13, a.;) secondly, the foliated character of the margin of the transverse plates, at the junction with the external shell. (Pl. 44, Fig. 5, 8, 12, 13.) The external shell of Hamites is also fortified by transverse folds or ribs, increasing the strength both of the outer chambers and of the air-chambers, upon the same principles that we have pointed out in the case of Ammonites. (See Pl. 44, Fig. 8, 9, 11, 12, 13.)

In certain species of Hamites, as in certain Ammonites, the marginal Siphuncle has a keel-shaped pipe raised over it. Others have a series of spines on each side of the back. (Pl. 44, Fig. 9, 10.)

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borough. (See Phillips' Geology of Yorkshire.) Some of the larger species equal a man's wrist in diameter.*

Scaphite.

The Scaphites constitute a genus of Elliptical chambered shells, (see Pl. 44, Fig. 15, 16,) of remarkable beauty, which are almost peculiar to the chalk formation; they are so rolled up at each extremity, whilst their central part continues nearly in a horizontal plane, as to resemble the ancient form of a boat; whence the name of Scaphite has been applied to them.†

It is remarkable that those approximations to the structure of Ammonites which are presented by Scaphites and Hamites, should have appeared but very rarely, and this in the lias and inferior oolite, until the period of the cretaceous formations, when the entire type of the ancient and long continued genus Ammonite was about to become extinct.

Turrilite.

The last genus I shall mention, allied to the family of Ammonites, is composed of spiral shells, of another form, coiled

* The Hamites grandis, (Sowerby, M. C. 593,) from the Greensand at Hythe, is of these large dimensions.

+ The inner extremity of the Scaphite is coiled up like that of an Ammonite, (Pl. 44, Fig. 15, c. and 16) in whorls embracing one another; the last and outer chamber (a) is larger than all the rest together, and is sometimes (probably in the adult state) folded back so as to touch the spire, and thereby materially to contract the mouth, which is narrower than the last or outer chamber. (Pl. 44, Fig. 15, b.) In this character of the external chamber, the Scaphite differs from the Ammonite; in all other respects it essentially agrees with it; its transverse plates being numerous, and pierced by a marginal Siphuncle, at the back of the shell (Fig. 16, a.;) and their edges being lobated, deeply cut, and foliated. (Fig. 15, c.)

The Scaphites bifurcatus occurs in the Lias of Wurtemburg, and Hamites annulatus in the Inferior oolite of France.

around themselves in the form of a winding tower, gradually diminishing towards the apex (Pl. 44, Fig. 14.*)

The same essential characters and functions pervade the Turrilites, which we have been tracing in the Scaphites, Hamites, Baculites, and Ammonites. In each of these genera it is the exterior form of the shell that is principally varied, whilst the interior is similarly constructed in all of them, to act as a float, subservient to the movements of Cephalopodous Mollusks. We have seen that the Ammonites, beginning with the Transition strata, appear in all formations, until the termination of the Chalk, whilst the Hamites and Scaphites are very rare, and the Turrilites and Baculites do not appear at all, until the commencement of the Cretaceous formations. Having thus suddenly appeared, they became as suddenly extinct at the same period with the Ammonites, yielding up their place and office in the economy of nature to a lower order of Carnivorous mollusks in the Tertiary and existing seas.

In the review we have taken of genera in the family of Chambered shells, allied to Nautilus, and Ammonite, we have traced a connected series of delicate and nicely adjusted instruments, adapted to peculiar uses in the economy of every animal to which they were attached. These all attest undeviating Unity of design, pervading many varied adaptations of the same principle; and afford cumulative evidence, not only of the exercise of Intelligence, but also of the same Intelligence through every period of time, in which these extinct races inhabited the ancient deep.

* The shells of the Turrilites are extremely thin, and their exterior is adorned and strengthened (like that of Ammonites,) with ribs and tubercles. In all other respects also, except the manner in which they are coiled up, they resemble Ammonites; their interior being divided into numerous chambers by transverse plates, which are foliated at their edges, and pierced by a siphuncle, near the dorsal margin. (Pl. 44, Fig. 14, a, a.) The outer chamber is large,

SECTION VII.

Belemnite.

WE shall conclude our account of chambered shells with a brief notice of Belemnites. This extensive family occurs only in a fossil state, and its range is included within that series of rocks which in our section are called Secondary.* These singular bodies are connected with the other families of fossil chambered shells we have already considered; but differ from them in having their chambers enclosed within a cone-shaped fibrous sheath, the form of which resembles the point of an arrow, and has given origin to the name they bear.

M. de Blainville, in his valuable memoir on Belemnites, (1827) has given a list of ninety-one authors, from Theophrastus downwards, who have written on this subject. The most intelligent among them agree in supposing these bodies to have been formed by Cephalopods allied to the modern Sepia. Voltz, Zieten, Raspail, and Count Münster, have subsequently published important memoirs upon the same subject. The principal English notices on Belemnites are those of Miller, Geol, Trans. N. S. London, 1826, and that of Sowerby, in his Min. Conch. vol. vi. p. 169, et seq.

A Belemnite was a compound internal shell, made up of three essential parts, which are rarely found together in perfect preservation.

First, a fibro-calcareous cone shaped shell, terminating at its larger end in a hollow cone (Pl. 44, Fig. 17. and Pl. 44', Fig. 7, 9, 10, 11, 12.†)

*The lowest strata in which Belemnites are said to have been found is the Muschelkalk, and the highest the upper Chalk of Maestricht.

This part of the Belemnite is usually called the sheath, or guard: it