Lign. 204. Fossil Teeth and Jaws of Fishes. Chalk. Sussex.
| Fig. | 1.— | Tooth of Saurocephalus lanciformis. Lewes. |
| 2.— | Teeth of Saurocephalus striatus. Brighton. Portion of the jaw, with five teeth. | |
| 3.— | Fragment of a jaw, with two perfect teeth, and the base of another, of Saurodon Leanus. Kemptown, Brighton. | |
| 4.— | Enchodus halocyon. Left branch of the lower jaw, with teeth; and one front tooth of the opposite portion. Lewes. |
M. Agassiz retains the names imposed by the American naturalists, and has placed these genera in the family of Scomberoids (Mackerel, Swordfish). They belong to the Pharyngognathi of Muller. The teeth are disposed in a single row, and fixed in deep sockets by a simple root, or fang, which is frequently somewhat excavated by the pressure of a successional tooth. In Saurodon Leanus the crown of the tooth is angular, and barbed, and supported on a sub-cylindrical shank, or stem (see [Lign. 204], fig. 3). The microscopical structure of these teeth presents that peculiar reticulated disposition of the medullary canals throughout the entire body of the tooth, which is only found in the dental organs of fishes.
Hypsodon Lewesiensis. (Foss. South D. tab. xlii.)—The Sussex and Kentish Chalk also contain the remains of a very large fish, belonging to the Pharyngognathi, with extremely upright, long, conical, compressed, pointed teeth, which, like those of the Saurodon, are implanted in sockets. These teeth are commonly of a delicate fawn colour externally and of a dark brown internally; having a large simple pulp-cavity. In Foss. South D. (tab. xlii.) are represented portions of an intermaxillary and jaw-bone with teeth; a vertebra, deeply biconcave; and a large bone, apparently a branch of the os hyoides; all found in the same block of chalk.[563]
[563] A magnificent specimen (now in the British Museum) displays, on the same slab of chalk, a large portion of the cranium, teeth, several vertebræ, ribs, and many other bones, belonging to a fish of considerable magnitude. Petrif. p. 444.
Enchodus (sword-tooth) halocyon. [Lign. 204], fig. 4. (Poiss. Foss. tom. v. tab. xxvc.)—The specimen figured is a portion of the lower jaw, with one row of elongated, conical, slightly curved, pointed teeth; the two anterior teeth being much longer and larger than the others; it affords a good illustration of the dental organs of Enchodus; a genus of Acanthopterygian fishes, the jaws and teeth of which are often found in the Sussex Chalk. The teeth are of various sizes, and attached by anchylosis, one row on the premandibular bone, and another irregular row of smaller teeth to the inside of the lower jaw. The two anterior teeth are very large, and of a peculiar form: their base is wide and solid, and the shank of the tooth is suddenly contracted immediately above, and becomes elongated into a point. These teeth are generally of a dark colour, have a glossy aspect, and are very brittle; differing so remarkably in this respect from the shark’s teeth, with which they are usually collocated, that mere fragments can be readily identified. The external surface of the lower jaw is marked with finely granulated, longitudinal ridges or striæ.[564]
[564] A fine example of the lower jaw, with twelve teeth, is figured Foss. South D. tab. xli. and another, with the upper jaw and teeth, Geol. S. E. p. 140. Beautiful figures of the remains of Saurocephalus, Enchodus, Hypsodon, and many other fine Chalk fishes, are given in Dixon’s Fossils of Sussex, 4to. 1850.
Mr. Toulmin Smith, of Highgate, has in his Museum a portion of the lower jaw with fifteen teeth of a small individual, imbedded in the centre of a flint nodule, from Gravesend, which was discovered by accidentally breaking the stone. The bone of the jaw and the teeth are of a dead white colour, and appear not to be in the slightest degree silicified; but in those teeth which are broken the pulp-cavity is filled with quartz, which must have transuded through the walls of the teeth.
Ichthyolites of recent species.—The distinguished naturalist to whose labours in fossil Ichthyology we have been so largely indebted, states, that of the many hundred species submitted to his notice, but one can be identified with any fish now living. This conclusion must, however, be received with some reservation; for, among the fossil genera, founded on the teeth, there are species which certainly cannot be distinguished from recent forms. And in the diluvial drift at Breslau, associated with the bones of the fossil elephant (Elephas primigenius), the remains of a pike, closely resembling the common European species, have lately been discovered.[565]
[565] Agassiz, Poiss. Foss. tom. v. p. 68.