and is sent in larger quantity into the extremities, and where, in consequence, the excess of heat is conveyed and expended, and its accumulation in the central and deepseated organs prevented, affording another striking example of harmonious adaptation.

The same thermometer was employed in making all the observations described in this paper; and in every instance, in stating the results, allowance has been made for error in its graduation, carefully determined by comparison with a standard instrument, one belonging to Professor FORBES of Edinburgh, and for the use of which I have been indebted to his kindness.

The Oaks, Ambleside,

Nov. 1st, 1843.

VI. A Description of certain Belemnites, preserved, with a great proportion of their soft parts, in the Oxford Clay, at Christian-Malford, Wilts. By RICHard Owen, Esq., F.R.S., &c.

Received March 14,-Read March 21, 1844.

THE extinct Cephalopod, called Belemnite, has long been known by its peculiarly complex shell, which includes a part possessing the chambered and siphonated structure characteristic of the entire shell of the Spirula and Nautilus, and the fossil Orthoceratites, Baculites, Ammonites, &c. Like the latter unequivocal congeners of the still existing Nautilus, the Belemnites are distributed through a vast series of the secondary rocks from the epoch of the muschelkalk, when they seem first to have been introduced into the old ocean of this planet, up to the Maestricht chalk, when they finally perished.

No fossil shell has more exercised the ingenuity and research of the interpreters of ancient Nature, or has given rise to so many conflicting opinions as to the affinities of its animal constructor, than the Belemnite: but the specimens from the Oxford clay near Christian-Malford, in Wiltshire, liberally presented by the Marquis of NORTHAMPTON, P.R.S., SAMUEL PEACE PRATT, Esq., F.R.S., and WILLIAM JOHN Broderip, Esq., F.R.S., to the Royal College of Surgeons, leave no reasonable ground for further hesitation or scepticism on the subject, since they display in a truly marvellous manner, those soft and seemingly most perishable parts of the animal which are essential to convey a true idea of its living form.

It must, however, be premised in vindication of the fruitful principle of physiological correlations, established by CUVIER as the key to the interpretation of fossil remains, that, for some years prior to this discovery, there had been obtained sufficient evidence of the organization of the Belemnite, to determine both its ordinal and family affinities; but, as the value of this evidence failed to be appreciated by some experienced palæontologists, from want of sufficient knowledge of, or faith in, the laws of the interdependencies of the characteristic parts of the Cephalopodal organization, the additional facts afforded by the well-preserved specimens from the Oxford clay are most acceptable and valuable.

In the compound shell of these specimens the following parts are recognizable :

1st. The terminal spathose body called the 'guard,' sheath or rostrum *, resembling the head of a dart or javelin, whence the name Belemnite originally given to this part

of the shell, which is usually the only part preserved, and now extended in its application to the entire animal.

2nd. The chambered or siphonated part of the shell which I have called the phragmocone*,' and which is lodged in the conical alveolus or cavity at the base of the 'guard.'

3rd. The conical, thin, but dense, corneo-nacreous case, which immediately invests the phragmocone, and lines the alveolus of the guard; commencing at the bottom or apex of that cavity, and continued beyond the thin margins of the basal aperture of the alveolus, and beyond the last septum of the phragmocone, to form, as Dr. BUCKLAND rightly describes, the large anterior chamber of the Belemnite containing the ink-bag and some other viscera.

The numerous species of Belemnite have been classified according to the modifications of the spathose guard; the one under consideration belongs to the group characterized by a rounded, elongated, conical guard, with a short, terminal, ventral, longitudinal impression; it was first recognised as a new species by Mr. PRATT, who has honoured me by naming it Belemnites Owenii. This species approximates in its general form to the Belemnites elongatus and Bel. longissimus of MILLER, from the lias; but it presents intermediate proportions of length to breadth, and maintains the same diameter throughout a much greater part of its extent; the anterior expansion, which is very gradual, commencing, nevertheless, nearer the alveolar extremity, and ending less widely. The excavated part of the guard becomes very thin as it expands, and, there having been no infiltration of mineral matter into its cavity, or into the chambers of the phragmocone, it has yielded to the pressure of the superincumbent strata, and thus in its flattened and fractured state shows a greater degree of expansion than is natural to it. The thin and brittle margin of the spathose alveolus may be traced nearly half way towards the base of the phragmocone, which is there invested only by the thinner and more yielding corneo-nacreous sheath §.

The gradual expansion of the guard from its posterior end or apex is shown in the figure 1. The ventral groove (fig. 2 a') extends to about one-fourth the length of the guard, commencing a little in advance of the apex: it is very shallow, with the

Pl. II. figs. 1 c, 6, 7 and 8. payμòs partition, Kŵvos cone.

Lectures on Comparative Anatomy, 8vo, 1843, p. 333. The term 'alveolus' has usually been applied to the chambered cone; but it appears better to restrict it to the socket in which the chambered cone is lodged.

Pl. II. fig. 6, and fig. 7, 7.

Bridgewater Treatise, 1836, p. 372.

In the specimen of Belemnites elongatus figured by MILLER (Geol. Trans. 1826, Pl. VII. fig. 6.), this thin sheath, which extends beyond the wider part of the alveolus, had perished, as is usually the case, and the casts of the chambers of the phragmocone, which is preserved in situ, are exposed. To this is due the appearance which M. DE BLAINVILLE was unable to understand in the figure above cited. "Ce que je ne conçois pas dans cette figure, c'est la manière dont les calottes empilées, qui constituent l'alvéole, dépassent de beaucoup la cavité de la coquille ou du tube, dont les bords sont cependant assez amincis pour croire que le péristome est parfait."-Sur les Belemnites, p. 95, 4to, 1827.