« ZurückWeiter »
is, I believe, the Carex uliginosa of Suter, not Linnæus; but was made
- paniculata, Linn. In the osier beds near the Cherwell below En-
ampullacea, Gooden. In the Peat-pits, common. MYRIOPHYLlum verticillatum, Linn. In ditches in the meadows between
the Oxford canal and the Cherwell, particularly near the swing bridge. Salix pentandra, Linn. A tree, bearing sterile catkins, of this beautiful
species of willow, hangs over the spring in Oldbury, and when in flow-
Art. IX.-Illustrated Zoological Notices. By EDWARD CHARLES
WORTH, F.G.S., &c.
( Continued from Vol. i. n. s. p. 534.) On the Fossil Remains of a Species of HYBODUS, from Lyme Regis. Our acquaintance with the zoological history of the defensive fin-bones termed Ichthyodorulites, both as it respects their specific determination and the group of fishes to which they appertain, is principally due to the labours of Louis Agassiz: and a considerable portion of the work now in course of publication by this eminent naturalist,—the 'Recherches sur les Poissons Fossils,'—is devoted to the illustration and description of these interesting fossils. Ranging vertically from the deposits of the cretaceous period to those of the Silurian system, and horizontally throughout an area of probably unlimited extent, the Ichthyodorulites, owing to their bony texture and exterior of enamel, have been preserved during the long period of their entombment with singular fidelity: and when disinterred from their matrix, assisted by a knowledge of the teeth, with which these osseous rays were formerly associated, the ichthyologist may safely venture to infer their relation to existing types, though all other traces of the skeleton may have disappeared.
The genus Hybodus is spoken of by Agassiz as being perhaps the most important of the extinct genera of placoid or cartilaginous fishes, in which one or both dorsal fins were armed with these defensive weapons. A large number of species are already characterised in the 'Poissons Fossils,
the greater portion of which appear to have existed during the deposition of the secondary rocks of this country. In 1822 Mr. De la Beche figured a spine and jaw of this genus in the “Transactions of the Geological Society;' but fossil Ichthyology had at that time received little attention, and even up to a much more recent period, the Ichthyodorulites were erroneously imagined to belong to genera allied to Balistes or Silurus, although a comparative
examination of the basal termination of these organs would have readily shown the incorrectness of the supposition. Agassiz, in his general observations upon the Ichthyodorulites, acknowledges the valuable assistance which he received from a manuscript paper by Dr. Buckland and Mr. De la Beche, containing the descriptions of twelve species; and he remarks that the authors of this paper had then arrived at a knowledge of the true affinities of the rays in question.
A few weeks since Mr. Edmund Higgins, of Cheltenham, a gentleman who has for some time been a very ardent collector of fossil remains, brought for my inspection the beautiful specimen which forms the subject of these observations, the joint discovery of himself and Miss Anning, in the lias of Lyme Regis. Appearing to be the most perfect jaw of the Hybodus I had yet seen, and to possess a feature altogether new to the genus, in the presence of a curved spine about the region of the head, I requested and readily received permission from its owner to draw up the present notice for the Magazine of Natural History.'
The specimen consists of two tabular masses, (see Supplementary Plates, No. 4, fig. 1 & 2), on which the teeth are arranged in a regular series. The larger fragment (of which, in the engraving, some portion is omitted) is of a quadrate shape, and from half an inch to three quarters in thickness. Its anterior border is raised, slightly curved outwards, and bristled with teeth, which are disposed along it in parallel rows six deep, the external row being placed upon the extreme edge. The remaining three borders have abruptly broken edges, and from the section of the interior thus displayed, the mass, with the exception of a part of the jaw forming the anterior border, appears to consist of folds of skin and portions of bone, probably of the head, compressed together; but the whole is so blended with the lias which has filled the interstices, as to render the separation or discrimination of the parts a matter of impossibility. On one surface, however, of the mass, the opposite to that represented in the plate, a considerable portion of the skin is preserved apparently uninjured, and it is seen thickly beset with beautifully enamelled coni
cal studs, each of which is attached by a neck to a round and expanded base, (fig. 5, 6 & c). The surface of these dermal points is marked with very prominent costæ, and their substance appears to be exactly analogous to that of the teeth. The portion of the skin of Acrodus, an allied genus, figured in Dr. Buckland's Bridgewater Treatise, seems to present a closely analogous character.
Notwithstanding that the teeth in this specimen are very numerous, and for the most part implanted in the bone by their original attachments, I have been quite unable to form an idea respecting the character which the entire jaws would present, and the relations which they have borne to the surrounding parts. The fragments of jaws figured by Agassiz, throw no light upon this matter; and although in the Poissons Fossils' a great many species are characterised by the osseous spines, and the genus often alluded to in the remarks upon Ichthyodorulites, the complete history of its characters and probable affinities has as yet been postponed."
I am not able to determine whether the two fragments figured belong to one and the same side of the mouth, or to the upper and lower jaws: there is nothing like a symphysis, nor at the termination of the rows do the teeth present any decided diminution in size or number, by which the position of the lateral ligamental articulations might be detected.The series of teeth on the larger fragment consists of seven rows, six deep, disposed along the anterior border of the mass; at one extremity the continuity of the series being interrupted by the fractured lateral edge or border of the mass itself, the rows of teeth are continued nearly to the margin of the opposite lateral border, but here they make a sudden bend inwards and backwards, by which their continuity is preserved; the portion so recurved consists of five additional rows, and its termination about the centre of the mass is shown in the figure. Reasoning from the analogy of the jaws in the existing genera of sharks, and also from the apparently forcible displacement of the teeth at the immediate spot where the bend occurs, this sudden curve would appear to be the result of accident, rather than the natural disposition of the parts. The smaller fragment however exhibits a very similar and equally sudden alteration in the direction of the rows of teeth, and the same thing may be observed in the original jaw figured by M. de la Beche in the 'Geological Transactions.'
1 I believe the 12th livraison of the ‘Poissons Fossils' is very shortly expected, and it may possibly contain the history of the genus Hybodus.
A very strong and irregularly shaped bone arises from the centre of the mass, and, with its base apparently resting upon this bone, is placed the curved spine which constitutes the principal feature of interest in the present specimen.From the position which this spine now occupies, it would appear to have been situated about the region of the head, bending abruptly forwards directly it emerged from the integuments. The apex of the spine is unfortunately broken off; but the portion left is about half an inch long, covered with a smooth glistening coat of enamél, and presenting a slight but well-defined upper edge. A few elevated and wavy strie are irregularly distributed upon its surface. The spine arises from a strong, expanded, bony base, which is formed by three obtuse processes united in a common centre, one of them extending anteriorly in the median line, and the other two, which may be termed the lateral processes, at right angles to the anterior one. Some portions of the surfaces of these processes would appear to have given attachment to very strong muscles, (fig. 7 & 8).
At the first glance this hooked spine might be thought to be related to those which characterise so many species of the genus Raia of Linnæus, but its remarkable bony base, and the general aspect of the organ itself, would seem to indicate its connexion with more important functions than are possessed by a mere dermal prickle. In the absence of evidence to the contrary, I should feel disposed to regard it as a solitary spine, developed in the median line of the frontal region, and connected with or simply resting upon the bones of the cranium. In the Chimera monstrosa, to which Hybodus has some affinity, a horn or frontal process is also present. In this instance, however, it is only found in the male sex, and the process itself has none of the formidable character about it presented by the spine of Hybodus ; having but a comparatively slight base, and though the apex is armed with a series of small prickles, the process itself is, I believe, externally fleshy, with an internal, slight, bony support. The apparent analogy, however, is worth a passing notice, because the teeth of Chimera, although an existing genus, have been found fossil in deposits which also contain the remains of Hybodus.
The teeth in the present specimen vary from half an inch to three quarters of an inch in length. They are slightly bowed, with the convexity outwards, and at ihe same time arched from above to below, so that the apices of the outermost lateral lobes, in many instances, are nearly on the same level with the base of the central process. The crown of the tooth slightly projects beyond the osseous root which con
nects it with the jaw, the line of separation being marked by a well-defined sulcus. The crown is composed of a central conical, blunt process, bounded on either side by four or five small lobes, which are more or less distinctly developed. A raised median line extends from the apex to the base of the central process, both on the inner and external aspects, giving off other lines, which diverge,' and spreading over the rest of the process, become suddenly thickened just before they reach its base. Upon the smaller processes or lobes of the teeth, the lines also exhibit a strong tendency to converge towards the large central one. The space between these raised lines is about double that occupied by the lines themselves. On the internal aspect of the teeth, the lines exhibit, in a greatly diminished degree, the tendency to converge towards the central process, (see fig. 4). In many of them indeed, over the internal surface, the lines are vertical in their direction. Below, and extending parallel to the groove which separates the crown from the osseous root, is a prominent ridge, (see fig. 3), but of this there is no corresponding indication on the internal aspect, (fig. 4).
The above description must be considered as applying to the apparently normal or typical character of the teeth, many modifications of which may arise from their position in a particular part of the jaw, or from accidental circumstances.
The teeth, as shown in the figure, appear to have been uniformly directed backwards and inwards, and the lowest row in the series lies quite flat, as in the recent genera Galeus, Carcharias, &c. A circumstance worth notice is that the lowest row in the series is shown, by fractured specimens, to be fully as capable of taking office as those occupying the front rank; now the corresponding teeth in many existing squaloid genera are mere hollow cases, which become gradually filled with osseous matter as they ascend in the series.
I have been led rather minutely to detail the characters presented by this fossil jaw, because so large a number of species are included in the genus, and also because I have not been able to refer it to any species hitherto described.— Agassiz has figured the teeth of three species of Hybodus from the lias of Lyme Regis and Bristol, namely, Hyb. raricostatus, reticulatus, and medius. The teeth of the present species differ from the first of these in the greater size of the central process, and the less distinct development of the lateral ones, and in presenting much more numerous and small
1 The divergence of these lines is best shown by the recumbent teeth about the middle of the anterior border of the larger fragment, (fig. 1).