Lign. 195. Outline of the Dapedius. Lias. (1/2 nat. size).
Dapedius. [Lign. 195].—At Lyme Regis, and other productive localities of the fossils of the Lias, large masses of angular enamelled scales, and occasionally entire specimens of the fishes to which they belonged, have for many years been collected. Sir H. De la Beche first scientifically investigated the structure of these Ichthyolites, and pointed out their characters and relations. The Dapedius (of which a restored figure is given in [Lign. 195]) is a flat, laterally compressed fish, with a rounded head, and fins of moderate size. The body rapidly contracts towards the root of the tail, the fin of which is large and symmetrically lobed. The mouth is furnished with several rows of small conical teeth, which are crenated at their summits, and has brush-teeth on the palatine bones; the jaws are short. The scales are rhomboidal, highly polished, and united laterally by short processes; as in many other ganoid fishes. It belongs to the Lepidoids.
The Tetragonolepis is a Liassic fish, very similar in shape to the Dapedius. It was formerly grouped with the Lepidoidei, but Sir P. Egerton has lately discovered that it essentially differs from those fishes in the character of its scales and teeth, and that it belongs to the Pycnodonts.
Lepidotus.[536] [Lign. 186], 196, 197.—Scales of a dark-brown, almost black colour, with a glossy enamelled surface, and of a rhomboidal or lozenge form, and teeth equally dark and glossy, of an obtuse hemispherical figure, are very common in the Wealden strata of the south-east of England and in the Isle of Purbeck. They are called by the quarry-men fishes' scales and eyes. The collectors of the last century used to term the obtuse circular teeth of this and the related genera Bufonites, from a supposition that they were formed in the heads of toads. These relics belong to an extinct genus named Lepidotus, which contains numerous species, that are distributed in the Oolite, Purbeck, and Wealden formations. These fishes resembled the Carps in their general form, but they have no anatomical relations to that family. The body is covered with large rhomboidal scales, which are protected on the external surface by a thick plate of enamel (Lign 196, fig. 3). The lateral line, which is slightly arched, passes direct from the operculum to the middle of the insertion of the caudal fin. The head, and even the face, are cased with osseous and enamelled plates. The bones of the surface of the skull are very large, and are connected by sinuous sutures. The jaws are short and rounded, and furnished with a row of obtuse, conical, circular teeth (see [Lign. 197]), and several rows of sessile teeth, more or less contracted at the base, which forms a very short pedicle that is anchylosed to the bone. The fossil Lepidoti are found, for the most part, in fluviatile deposits, as in the Purbeck and Wealden strata; and it is probable they inhabited the rivers or sea-coasts, and not deep waters.
[536] Poiss. Foss. tom. ii. p. 233.
Lign. 196. Scales and Fin of Lepidotus Mantelli. Wealden.
Tilgate Forest. (Nat. size.)
| Fig. | 1.— | Scale, with a single process of attachment. |
| 2.— | One of the scales of the dorsal line. | |
| 3.— | Scale (external surface), with a bifurcating process of attachment;the enamelled portion (which alone is visible whenthe scales are in their natural position on the animal) haslongitudinal grooves or folds. | |
| 4.— | Scale (viewed on the inner surface), having a bifurcatingprocess of attachment and a tooth or projection on each side,to connect the scale laterally with the adjoining scales. | |
| 5.— | The front ray of the dorsal fin, covered with two rows ofenamelled scales, and another ray behind it. |
The scales and teeth figured [Lign. 196], 197, belong to the larger species of the Wealden. The remains of this fish were first collected in Tilgate Forest, and several teeth and: scales are figured Foss. Til. For. pl. v. and x.; considerable portions of connected scales have since been found; also the head entire, and the fins more or less perfect. A specimen in my collection retained a mass of the scales near the insertion of the tail, a foot wide; indicating the original to have been twelve feet long, and its body three feet broad. The scales are distinguished from other species by the folds or grooves on their enamelled surface; and the teeth by the contracted base, or pedicle, which is a little narrower than the crown ([Lign. 197], and [Pl. VI. fig. 10]). A species (L. Fittoni) closely related to the above is equally abundant in the Weald of Sussex; the scales are not striated, and the teeth have no pedicle.