stratum and restricted locality, admits of no reasonable doubt of their belonging to one and the same species of true Belemnite. The two flattened fibrous bodies, (e, e) with well-defined semi-oval external and apparently free margins, the one on the right side entire, the one on the left having the contour of the defective part of the margin indicated by the dark carbonaceous stain in the matrix,—are the parts which I regard as the lateral fins of the mantle. They have been slightly displaced transversely and pressed inwards upon the yielding viscera; their original cartilaginous basis would favour their encroaching in that direction if subjected to equable surrounding pressure: the lateral fin which is preserved in the first specimen* has been pushed more deeply inwards. The large end of the semi-oval free border is the anterior one, where the fin is broadest; it gradually becomes narrower posteriorly. The muscular fasciculi are strongly marked, and are arranged transversely to the long axis of the fin, as in existing Decapodous Cephalopods. It is interesting to find a rounded contour associated with an advanced position of the lateral fins in the ancient Belemnites, as in the modern Rossia and Sepiola, the rhomboidal form being most common in those fins which are placed at the end of the body, as in the Onychoteuthis and Loligo; the only exception, indeed, being presented by the Loligopsis, which has terminal and rounded fins. M. DUVAL, the latest and most accurate author on fossil Belemnites, reproduces† the figure which M. D'ORBIGNY has published, and which is essentially the same as that given by Dr. BUCKLAND in his Bridgewater Treatise; and, like it, differs from Mr. MILLER'S restoration, in the position of the ink-bag and in the extended state of the terminal fins. With respect to these parts, M. DUVAL, from his discovery of the united fractures of the spathose guard, has objected with much acumen, that, if the fins of the Belemnite had been placed at the side of the guard, they must have been rendered useless by its fracture, and the creature, thus deprived of its power of swimming, would soon have fallen a prey to its numerous enemies, and would not have survived to exemplify the reparative powers of those ancient Cephalopods. M. DUVAL, however, modestly concludes by confessing that he should not have dared himself to figure from the known analogies, the animal to which the Belemnite ought to have belonged; for "I have not," he says, "a sufficiently exact knowledge of the organic laws of the Cephalopoda." It seemed vain to hope that the soundness of the principles on which the classification of the Belemnites with the dibranchiate Cephalopods had been definitely proposed, should ever be vindicated by the demonstration of parts, apparently so perishable as the fleshy mantle, the fins, and the slender flexile arms of these ancient Molluscat. * Pl. III. + Sur les Belemnites, 4to, Pl. 7. fig. 10. CUVIER, in the second edition of the 'Règne Animal,' places the Belemnites between the Orthoceratites and the Ammonites, and observes, "ils appartiennent probablement encore à cette famille, mais il est impossible de s'en assurer, puisqu'on ne les trouve plus que parmi les fossiles," tome iii. p. 19,-which teaches how liable the best authorities are to err, when they would set bounds to the possibilities in Nature. But we derive from the present remarkable specimens ample confirmation of the association of the ink-bag with the higher grade of the circulating and respiratory organs, which grade is necessarily associated with the high development of the locomotive system, as demonstrated by the muscular mantle and its appended fins; whilst the preservation of the latter organs in situ establishes the soundness of M. DUVAL'S objections to their position in all the published conjectural restorations of the Belemnite. In the specimen under consideration* the fins are crossed by a narrow tract of grey transversely fibrous substance, probably part of the mantle, near the anterior termination of which an oblong flattened tract of similar substance extends forward, slightly expanding as it advances to a position opposite the neck of the Belemnite, where it is terminated by a slightly concave truncation: longitudinal fibres may be discovered decussating the more abundant transverse fibres of the part which is most probably the remains of the infundibulum. A short flattened band of fibres (g) connects this part with the neck of the Belemnite, having the exact position and proportion of the retractor or levator muscles of the infundibulum of the naked Cephalopods. The traces of muscular tissue in the situation of the head are much more obscure: two short processes from the anterior part of this mass are evidently the bases of tentacula or cephalic arms. At the middle of the visceral mass, in the interval of the two lateral fins, there lies a compressed body of a horny texture and sub-bilobed form (m), on which may be clearly distinguished striæ passing outwards in opposite directions from a middle line and diverging from each other in their course, which resembles that of the fibres of the digastric muscle in the gizzards of the Nautilus and other Cephalopods: this apparent remnant of the stomach lies about half an inch in advance of the ink-bladder, in a position corresponding with that of the gastric organ in naked Cephalopods. There is strong negative evidence that the Belemnite possessed horny mandibles like the other naked Cephalopods, since no calcareous beaks, or Rhyncholites, have been discovered associated with the specimens from the Oxford clay, or with those from the lias. The thickness of the layer of dried and compressed grey fibrous matter to which the mantle is reduced is half a line, and we may infer from this, that in its soft and recent state, when permeated by its sanguiferous vessels, it must have equalled in thickness that of a Calamary of the same size. In fact the mantle of true Teuthida (Calamaries with horny pens), preserved in the same matrix as the Belemnites here described, has been reduced to a compact fibrous layer of the same thinness: a specimen of one of these displays by a fracture of the layer of the clay in which it was imbedded, the anterior and posterior walls with the intervening cavity of the abdomen, exposing the ink-bag and duct in situ. * Pl. IV. fig. 1. † Compare fig. 10, g, with CUVIER'S Pl. 1. fig. 2, m, n, Mémoire sur le Poulpe, 4to. |