Lign. 203. Smerdis minutus. Eocene. (nat. size.)
Aix in Provence.
Osmeroides. Plate II. and Wond. p. 344, 347.—Two species of this genus occur in the Chalk, near Lewes; and principally, if not exclusively, in the Lower Chalk, without flints. They are exceedingly beautiful Ichthyolites, and are almost invariably found with the body but little compressed; the fish, in many examples, is as round and perfect as when living. The entire cranium, the opercula and branchial rays, and all the fins are preserved in some examples. These fishes belong to the Salmon family,[560] and are nearly related to the Smelt (Osmerus); whence the name of the genus. There are two species, easily distinguishable. The first (O. Mantelli, [Pl. II.]) has a short, sub-cylindrical body, and seldom exceeds eight or nine inches in length; the other (O. Lewesiensis) has an elongated and elliptical body, and sometimes attains a length of fourteen inches. The dorsal fin too in this species has more rays than in the other. The fossil figured in [Pl. II.]. is a very remarkable specimen of the first species. It is nine inches in length; and the chalk has been cleared away, so as to expose the entire fish, six inches in relief above the surface of the block, Petrif. Lign. 92, p. 445. The fish is lying on its back, with the mouth open, and the opercula, or gill-covers, and the branchial arches expanded; the pectoral and ventral fins, and the dorsal fin, are in their natural position; the five rays of the dorsal are erect; of the caudal fin, or tail, but slight indications remain. There is but one dorsal fin; but in a specimen of O. Lewesiensis there is a trace of the little adipose process observable between the dorsal fin and the tail, as in the recent species of Salmonidæ. A magnified view of one of the scales is represented [Lign. 185], fig. 4, p. 567.
[560] They were first described by me in Foss. South D. p. 235, tab. xxxiii. and xl. as Salmo Lewesiensis.
Of the Cyprinoids, or fishes of the Carp family (Malacopterygians), the recent species of which are inhabitants either of fresh-water, or the brackish waters of the mouths of rivers, many fossil species occur in the fluviatile and lacustrine deposits of the Tertiary formations. In their character of omnivorous fishes, the Carps then, as now, formed the principal mass of the finny population of the lakes, and in their turn served as food to the carnivorous tribes, as the pikes, eels, &c. Several species are found in a beautiful state in the schists of Œningen, and in the Tertiary marls at Aix. Many of the layers of marl at the latter locality are covered with groups of fishes of the family Cyprinodonts, the recent species of which are of a small size, and inhabit the fresh-water lakes of temperate zones. [Lign. 184], p. 562, represents a portion of a large slab of marl in the cabinet of Sir R. Murchison, which is covered with scores of a species resembling a recent fish (Lebias) in the profile of its head, and the form of its fins. It is named Lebias cephalotes, from the relative largeness of its head. The black appearance of the abdomen in many of these Ichthyolites indicates the original situation of the intestines and of the liver, which is largely developed in the fishes of this family, and contains much colouring matter.
Saurocephalus and Saurodon. [Lign. 204].—In the same quarry, near Lewes, from which the first entire fish of the Sussex Chalk was obtained, teeth of a very peculiar character were, many years since, occasionally discovered.[561] These teeth are of a lanceolate form, much compressed; with entire, sharp edges, terminating in a point; the fang is single, and broad; the surface of the crown is glossy, and marked with fissures filled with chalk (see [Lign. 204], fig. 1). Teeth of this kind, attached to portions of the jaw, were subsequently found in the Chalk at Brighton and Lewes. Similar remains were collected from the Cretaceous marls of Missouri and New Jersey, in the United States. The American specimens comprised two closely allied genera, which, from the supposition that the fossils were the relics of reptiles, were respectively designated Saurocephalus and Saurodon.[562] Examples of the teeth and jaws of both genera have been discovered in the Sussex Chalk (see [Lign. 204]).
[561] Foss. South D. tab. xxxiii. p. 228.
[562] American Phil. Trans, vol. iii. new series, pl. xvi. on the Saurodon, by Dr. Hays; and Journal Acad. Sciences, Philadelphia, vol. iii. on the Saurocephalus, by Dr. Harlan.
