The most perfect examples of the Pterodactyles have been discovered in the lithographic stone of Monheim, Pappenheim, and Solenhofen, where their bones are associated with the remains of Dragon-flies (see [p. 551]) and other insects. In England, bones of these reptiles have been obtained from the Lias of Lyme Regis, from the Oolitic slate of Stonesfield, from the Wealden strata of Tilgate Forest, and the Chalk of Kent.[675] One of the most interesting British specimens consists of a considerable part of the skeleton of a species about the size of a Raven, discovered by the late Mary Anning, in the Lias of Lyme Regis, and now deposited in the British Museum.[676] It consists of the principal bones of the extremities, and of several vertebra:, and is figured and described by Dr. Buckland, Geol. Trans. 2d ser. vol. iii. pl. xxvii. This specimen is distinguished by a greater length of the claws (whence the name of the species, P. macronyx, long-claw,) than in any previously known.
[675] For a detailed description of the Pterosaurian remains from the English Chalk, with numerous beautiful illustrations, see Prof. Owen s Monograph, published by the Palæontographical Society, 1851. Other important memoirs on Pterodactyles and their structure, not mentioned in the text, are, by Von Meyer, in Nova Acta Acad. Nat. Curios. vol. xv. part ii. and Palæontographica, part i. 1846; Goldfuss, Nova Acta, vol. xv. part i., and Reptilien der Vorwelt, 1831; Prof. Owen Quart. Journ. Geol. Soc. vol. iii. and Mr. Bowerbank, ibid. vol. iv.
[676] See Petrif. p. 189.
The remains of the Pterodactyles of the Chalk, for the most part, indicate a large size for the original animals. It has been estimated that some of these gigantic flying reptiles possessed an extent of wing surpassing that of the great albatross. The Pterodactylus Cuvieri had probably an expanse of wing not less than eighteen feet from tip to tip; another Chalk species, P. compressirostris, fifteen feet; whilst the P. macronyx, of the Lias, measured about four feet seven inches from the extremity of one wing to that of the other.[677]
[677] Bowerbank, Rep. Brit. Assoc. 1851, and Owen, Monograph, p. 104.
CHELONIANS.
VI. Chelonian Reptiles.—Those singular reptiles, commonly known by the name of Tortoises and Turtles, and designated by naturalists Chelonia (from Chelone, the Greek term for a Tortoise), are distinguished from all other animals by the osseous cuirass in which their bodies are enclosed, the head and neck, extremities, and tail, alone being excluded. This remarkable bony case is produced by the extraordinary development of the bones of the thorax and back; and consists of an under (sternal) and an upper (dorsal) portion. The breast-plate, or plastron, which is the true sternum, is composed of nine pieces of bone, eight of which are in pairs, and the ninth, or odd plate, is situated between the four anterior plates. The variation in the form of these plates is considerable, and affords important distinctive characters. In the young state of land and fresh-water tortoises, there are vacancies between the pieces, which are filled up in the adult, the whole being ultimately united into one bony plate; but in the marine turtles (and also in the Trionyces, or soft tortoises), these pieces do not completely unite, and interspaces always remain. The bones of which the dorsal buckler, carapace, or upper shield is composed consist of eight of the ten pairs of ribs, united by a longitudinal series of angular plates, which are attached to the annular part of the vertebra throughout the whole, or a great part of their length, according to the age and species of the individual.[678] Numerous modifications exist in the form of the buckler, in its flatness or convexity, in the degree of extension of the ribs, and their angular plates, and in the characters of the scutes or horny integument with which the carapace is covered; and with corresponding variations in the head, and in the locomotive extremities, in the numerous species and genera of the Chelonian reptiles, according to their adaptation to a terrestrial, fluviatile, or marine existence.
[678] In the Monograph on Eocene Reptiles, 1849, Prof. Owen has given a succinct account of the carapace and plastron of the Chelone, and a brief notice of the composition and homologies of these bony encasements in the Tortoise, with references to more particular and comprehensive memoirs by himself and others.
The animals of this order are arranged in four principal groups, viz. the marine, or Turtles (Chelones); the fluviatile, or river-Tortoises (Trionyces); the marsh-Tortoises (Emydes); and the terrestrial or land-Tortoises (Testudines). The marine Chelonians generally feed upon vegetables; the Emys and Trionyx approach more nearly to the terrestrial than to the marine species; they are carnivorous, feeding on frogs, fishes, fresh-water mollusca, and other small animals. The Trionyces differ from their congeners in being destitute of a horny external integument, having no scutes on the buckler or any other part of the body but the osseous carapace is invested with a strong tough skin, which equally covers the dorsum and sternum, to which it firmly adheres; the dermal surface of the bones in these Tortoises is always rugose, and either granulated, or covered with punctations and depressions. The buckler of the Trionyces is of a depressed form, with a soft flattened margin. The Testudinidæ, or land-Tortoises, are too well known to render any description requisite for our present purpose.
In the marine species, eight pairs of ribs and thirteen plates of the longitudinal series form the buckler; the ribs or costal plates are united to each other through a great part of their extent; but towards their distal or outer extremities each rib contracts, and terminates in a point, which is supported on a marginal series of bony plates; the intervals between the ribs are filled up in the living animal by a cartilaginous membrane which never becomes ossified. This character, therefore, affords an important aid in the discrimination of the fossil remains of this family.[679]