Lign. 239.
Beak or Mandible of a Turtle: nat. size.
Chalk. Lewes.
Among the numerous fossils obtained from the Chalk of Sussex, the only trace of a Chelonian reptile that has come under my observation is the bony mandible or beak of a Turtle, [Lign. 239]. Its surface displays a fibrous cancellated structure, denoting the attachment of the horny sheath with which, in a recent state, it was covered. More or less perfect specimens of such mandibles also occur in the Chalk of Kent and elsewhere, but no bones of the skull have yet been met with in that deposit. In the Greensand of Cambridgeshire, however, the cranium of a small turtle has been found. It is figured and described by Prof. Owen as Chelone pulchriceps (Monograph, 1851).
Chelone Bellii. [Lign. 240], Petrif. 155.—In the strata of Tilgate Forest, fragments of the carapace, of the plastron or sternum, and of the marginal plates, with some of the bones of the extremities, of a large marine turtle have been discovered; several specimens are figured in Foss. Til. For. pl. vi. and vii. Some examples must have belonged to an individual at least three feet in length. Unfortunately, the specimens hitherto obtained are very imperfect, and do not exhibit essential distinctive characters, with the exception of the ribs, which are united to within a short distance of their distal or marginal extremities; hence the costal interspaces are reduced to much smaller dimensions than in any recent or fossil Turtles with which I have had the means of comparing them. The fragment of a rib, imbedded in Tilgate grit, figured [Lign. 240], well exhibits this character.
Lign. 240. Chelone Bellii[688] (G. A. M.). Wealden. Tilgate Forest.
Portion of a costal plate, and the extremities of a rib: nat. size.
(Foss. Tilg. For. pl. vi. fig. 2.)
| a. | The striated pointed extremity of rib. |
| b. | The distal portion of the costal plate. |
[688] The remains of this reptile were noticed in the "Fossils of the South Downs, or Illustrations of Geology of Sussex," 4to. 1822, p. 47, and subsequently figured in the "Illustrations of the Geology of Sussex, with figures and descriptions of the Fossils of Tilgate Forest," 4to. 1827, p. 60, pl. vi. and vii.; and this extinct Chelone was regarded as a species, characterized by the great development of the rib-plates, and named after Professor Bell, the eminent zoologist, in the first Edition of the "Medals." But in the Monograph, Weald. Rept. 1853, this determination has lately been overlooked; and the specimen figured Tilg. Foss. pl. vi. fig. 2, is referred to the newly named Ch. costata, characterized by its broad and prominent ribs. A third name even (Ch. Mantelli) has been bestowed on this interesting fossil, by a German palæontologist.