Lign. 197. Portion of the Jaw of Lepidotus. Wealden. Tilgate Forest. (Nat. size.)
This specimen shows three successional teeth beneath a row of teeth in use.
The intimate structure of the teeth of the Lepidotus is beautifully preserved, and may be easily examined in thin transverse and vertical sections, viewed by transmitted light: see [Pl. VI. fig. 10]. The dentine is composed of bundles of tubes, continued from the cells of the osseous base, radiating in a vertical direction to the surface of the tooth, as seen in [Pl. VI. fig. 10], and giving off branches at an acute angle; but when more highly magnified, the finer branches are seen to be spread out and arched at their extremities, "presenting the appearance of the stems of corn, beaten down by heavy rain."[537]
[537] Odontography, p. 70. See the beautiful representation of this structure, pl. xxxi.
The dorsal and pectoral fins of these fishes are very strong, and consist of several bony rays. There is a double row of acuminated enamelled scales, arranged more or less obliquely, on the anterior margin of the dorsal and anal fins, and on both margins of the caudal: part of the first ray of a dorsal fin, with scales, is represented [Lign. 196], fig. 5.
A small species of Lepidotus (A. minor) is common in the Purbeck limestone, and specimens may often be procured from the quarries near Swanage;[538] it has also been found at Hildesheim, in Saxony, by M. Roemer. The detached scales abound in the limestones; and the splendid fossil reptile from Swanage, figured Petrif. Lign. 38, is sprinkled with the scales and minute teeth of this fish.
[538] Fine specimens of this fish are in the British Museum (Petrifactions, p. 429), and in the Museum at Dorchester.
The majority of the species of Lepidotus belong to the Lower Oolites and the Lias. The habits of the Lepidoti, as indicated by the form and structure of the teeth, were those of fishes whose food consisted of crustaceans, shelly mollusca, &c.; for the dental organs are peculiarly adapted for the crushing and grinding of such substances; and the teeth of the adult fishes are generally worn down by use.