Chapter 41

[671]The wordTelerpetonsimply denotes the remote antiquity of this Devonian reptile of Scotland, τἡλε (far off), ἑρπετον (reptile); the trivial name,Elginense, records the locality from whence it was obtained.[672]A model of this most delicate and valuable impression has been deposited in the palæontological gallery of the British Museum.[673]A general notice of the fossil foot-prints, orIchnolites, that have been referred to Reptiles will be given at a subsequent page of this chapter.

[672]A model of this most delicate and valuable impression has been deposited in the palæontological gallery of the British Museum.

[673]A general notice of the fossil foot-prints, orIchnolites, that have been referred to Reptiles will be given at a subsequent page of this chapter.

By reference toLign.235, it will be seen that the cranium is almost wholly lost; a few conical teeth, mostly of a very small size, were observed in connexion with the vestige of the jaws. The spinal column is represented by the impressions of about thirty-six vertebræ, eleven or twelve of which belong to its caudal portion. The vertebræ present some faint evidence of their possessing a biconcave form; the length of one of the dorsal vertebræ is1/9th of an inch. There are twenty-one pairs of long slender ribs. The pectoral arch and anterior extremities have nearly disappeared in the fracture of the stone. The pelvis and sacrum are very obscure; the latter is formed probably of two anchylosed vertebra;. The thigh-bones are somewhat curved; the tibia is gently bowed, and expanded at each extremity. There are no remains of the feet.

Lign. 235. Telerpeton Elginense (Mantell).Dev.Elgin.Impression of the skeleton (nat. size); showing the outline of the vertebral column, ribs, pelvis, femora, tibiæ and fibulæ, part of the caudal series of vertebræ, the left humerus, radius, and ulna, imperfect traces of the right anterior extremity, and obscure indications of part of the cranium.a.The remains of the cranium.b, b.Imprints of portions of the anterior extremities.c, c.Well-defined impressions of the thigh-bones and leg-bones, with an obscure sub-quadrangular pelvis.1.One of the teeth:nat. sizeandmag.

The structure of this reptilian skeleton, as far as the specimen can serve to show, indicates a peculiar type of organization, in which, as in numerous other extinct forms, in this, as in other Classes, osteological characters are associated which in existing oviparous quadrupeds are restricted to distinct orders and genera.

Lign. 236.Telerpeton Elginense (Mantell).Outline of the restored form of the original reptile:1/2nat.

Thelacertianaffinities of the Telerpeton are well marked in the relative size and form of the bones of its extremities, the situation of its pelvis, and probably in the articulation and the length of its ribs; but the contracted, biconcave centrum, and the short neural spine of the vertebræ, as well as the horizontality of the articulating surfaces of the zygapophyses, and the general uniformity of character throughout the spinal column, are to be regarded asbatrachianmodifications. Probably the original was a peculiar type, which, in the present state of our knowledge, it wouldbe rash to ascribe to either order. The length of the original animal could not have exceeded six or seven inches.Lign.236represents in outline the probable form of this small, but most interesting reptile.

V. Pterosaurians, or Flying Reptiles.—Pterodactylus(wing-fingered reptile).Lign.237.Petrif.p. 187;Wond.p. 577;Bd.pl. xxi. xxii.—The extinct reptiles denominated Pterodactyles, constituting a few genera of an order of Saurians organized for aërial life,[674]are unquestionably the most marvellous even of the wonderful beings which the relics of the Age of Reptiles have enabled the palæontologist to reconstruct. With a long-snouted head and long neck, much resembling that of a bird, bat-like wings, and a small trunk and tail, with lacertian affinities in its skull, teeth, and skeleton, and with a bird-like structure of sternum and scapular arch, these creatures present an anomaly of structure as unlike their fossil contemporaries, as is the duck-billed Ornithorhynchus, of Australia, to existing animals. The cranium, or brain-case, is small; the jaws are either long, and armed with numerous sharp-pointed teeth, or toothless, like those of a bird. The teeth of the Pterodactyle are all laniary; they are simple, of a conical form, recurved, with but little difference in their form and size, and implanted in distinct sockets, with wide intervals between each. In some species there are twenty-eight or thirty in the lower, and twenty-two in the upper jaw.

[674]The only known recent reptile at all analogous is the littleDraco volansof the East Indian Islands; but even this can scarcely be regarded as a flying animal, its lateral membranous expansions, which are rather parachutes than wings, and formed by elongated ribs, not by the fingers, presenting but a rudimentary condition of wings compared with those of the Bat and the Pterodactyle.

The orbit is very large; the sclerotica consists of an annular row of bony plates, but less in number than in theIchthyosaurus; the external orifice of the nostrils is near the orbits; remains of theos hyoides(bone of the tongue) have been observed.

Lign. 237. Pterodactylus crassirostris:1/2nat. size.Oolite.Solenhofen.

The cervical vertebræ are large and strong, and capable of great flexibility forwards and backwards, probably to allow the head to fall back to the centre of gravity during flight. There are frequently traces of ossified condition of the tendons of the muscles of the neck. This is well seen inP. macronyxandP. crassirostris(Lign.237), and is a peculiarity dependent on the additional support required by the long neck of the animal.

The dorsal vertebræ are from seventeen to twenty in number. The sacrum is formed by the coalescence of twovertebræ only, as in existing reptiles, and not of many, as in birds and certain extinct saurians. The tail is generally short, an unusual character with saurians; but a species with a long tail occurs at Solenhofen.

There are five toes or digits on each foot; the outer finger of the fore-arm is immensely elongated, for the support of a membranous expansion (the impression of this wing-membrane is preserved on the stone in some examples); and the other digits, of fore and hind feet, terminated in long curved claws. The size and form of the extremities show that thePterodactyluswas capable of perching on trees, of hanging against perpendicular surfaces, and of standing firmly on the ground, when, with its wings folded, it might crawl on all-fours, and walk or hop like a bird. A reference to the graphic description of the characters and probable habits of these beings, by Dr. Buckland,Bd.i. p. 221, and the beautiful illustrations accompanying it (Bd.ii. pl. xxi. xxii.), will equally instruct and gratify the reader.

The most perfect examples of thePterodactyleshave been discovered in the lithographic stone of Monheim, Pappenheim, and Solenhofen, where their bones are associated with the remains ofDragon-flies(seep. 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 specimensconsists 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 sMonograph, published by the Palæontographical Society, 1851. Other important memoirs on Pterodactyles and their structure, not mentioned in the text, are, by Von Meyer, inNova Acta Acad. Nat. Curios.vol. xv. part ii. andPalæontographica, part i. 1846; Goldfuss,Nova Acta, vol. xv. part i., andReptilien der Vorwelt, 1831; Prof. OwenQuart. Journ. Geol. Soc.vol. iii. and Mr. Bowerbank,ibid.vol. iv.[676]SeePetrif.p. 189.

[676]SeePetrif.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. ThePterodactylus Cuvierihad probably an expanse of wing not less than eighteen feet from tip to tip; another Chalk species,P. compressirostris, fifteen feet; whilst theP. 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 naturalistsChelonia(fromChelone, 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, orplastron, 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 importantdistinctive 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 theTrionyces, 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 theChelone, 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; theEmysandTrionyxapproach more nearly to the terrestrial than to the marine species; they are carnivorous, feeding on frogs, fishes, fresh-water mollusca, and other small animals. TheTrionycesdiffer from their congeners in being destitute of a horny external integument, having no scutes on thebuckler 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]

[679]The reader will recognise this peculiarity in the gilded skeleton of the carapace of Turtles, frequently exhibited in the soup-shops of the metropolis.

In the terrestrial and the marsh Tortoises, the ossification is complete in the adult state; but in the fluviatile Trionyces, which are without a horny integument, there is no border, or marginal series of bony plates, and the extremities of the ribs are therefore always distinct, and generally have an obtuse extremity. The skeletons of the three groups present corresponding modifications, and an accurate knowledge of the osteology of the recent animals is necessary to enable the palæontologist to arrive at secure conclusions as to the characters and relations of the fossil species.[680]We can only advert to one remarkable osteologicalcharacter,—the construction of the shoulder, which differs from that of all other animals, in being situated within the cavity of the thorax, instead of without. In consequence of this modification, a process of the shoulder-blade (scapulaoromoplate), termed theacromion, is largely developed, and the shoulder-bone is tri-mucronate, or three-pronged, consisting of a short, thick head, containing a concavity (which, with that on the coracoid-bone, forms a socket for the arm-bone), and of two diverging branches. This form is so peculiar, that the collector can be at no loss to recognise the shoulder-bone of aChelonian, should it come under his notice with other fossil relics (seeFoss. Til. For.pl. xix.fig.11). The shoulder-blade and its associated coracoid-bone undergo certain modifications in the three groups of Turtles, by which the anatomist may pretty certainly determine the terrestrial, fluviatile, or marine character of the animals to which they belonged. The successful application of a perfect knowledge of this department of osteology, is admirably exemplified in the works to which reference has been made; and even but a slight acquaintance with its principles will often enable us to obtain some general information as to the nature and relations of fossil Chelonians.

[680]The student should consult Cuvier’sOssemens Fossiles, tom. v. part iime.chap. ii.: and Prof. Owen’sMonographs, published by the Palæontographical Society, 1849, 1851, 1853. The Penny Cyclopædia,Art.Tortoises, contains an excellent summary of the osteology of these reptiles, also an abstract of Professor Owen’s Report on the FossilChelonia.

The student will remember that all the Chelonians are edentulous,i. e.toothless; their bony jaws being covered by horny sheaths, as in birds; these mandibles are therefore the only dental organs that can occur in a fossil state.

TURTLES AND TORTOISES.

Fossil Turtles and Tortoises.[681]—Some of the earliest indications of the presence of Reptiles on our planet are afforded by the foot-prints of Chelonian animals on the surfaces of the layers of sandstone of the Old Red formation at Elgin, and of the New Red in Dumfriesshire, at Storeton, near Liverpool, and at some places in Germany (seeBd.i. p. 259, and p. 265, note). But no osseous remains of the animals of this family have hitherto been found in strata antecedent to the Oolite. The Solenhofen quarries (Kelheim) have yielded the bones and carapaces of several Emydian tortoises, and some remains of Chelonians have been found at Stonesfield, and in the Portland Sandstone.[682]In the Jura limestone at Soleure, two large species of Emydians have been discovered. The Wealden and Purbeck formations abound in Chelonian remains of both fluviatile and marine genera. From the Isle of Purbeck numerous fine examples have been obtained;[683]my own researches in the strata of Tilgate Forest (Foss. Til. For.p. 60) have also brought to light several species, and in particular an interesting Chelonian related to the soft-skinned, fresh-water tortoises,Trionyces(Geol. S. E.p. 255). In the Cretaceous formation of England the remains of these reptiles are not frequent. The Greensand of Cambridgeshire (Rep. Brit. Assoc.1841, p. 172,) has yielded a marine species, and that of Kent a fine Emydian form (Owen,Monog.1851); and in the White Chalk a few examples have been obtained, to which we shall hereafter more particularly allude. On the Continent fine examples have been found in the slate of Glaris (seeBd.pl. xxv′.); and in the upper Cretaceous strata of the Netherlands, at Maestricht, and at Melsbroeck, near Brussels, many beautiful specimens of fresh-water tortoises (Emydes), and marine turtles (Chelones), have from time to time beenobtained; these are figured and described by Baron Cuvier (Oss. Foss.tom. v. pp. 236, 239). In the Eocene strata of England, several species of Chelonians have been collected; of these eleven belong to the marine genusChelone; eight to the fresh-waterTrionyx; and eight to the marsh-tortoises,EmysandPlatemys. The Isle of Sheppey and Hordwell have yielded the majority of these relics; the turtles are smaller than the recent analogues, which now inhabit intertropical latitudes.[684]The Eocene strata of France contain several fresh-water tortoises, some of which are referable to the Emydes, and others to the Trionyces. From the gypsum beds, near Paris, the remains of one or two species of Trionyx have been obtained (Oss. Foss.tom. v. p. 222), of another at Aix, in Provence, and of three or four species in other localities. A fine specimen of fresh-water tortoise from Œningen, near Constance, is described and figured by Professor Bell in Geol. Trans. 2d ser. vol. iii. The fossil remains ofTestudinidæ, or land-tortoises, are exceedingly rare. No well-determined remains are known in the British strata; the impressions of scutes found in the Stonesfield slate, and the foot-prints above described, being the only indications of the existence of these reptiles. The presence of land-tortoises in the strata of France appears to be equally problematical, for the relics obtained from Montmartre and Aix (Oss. Foss.p. 245) afford no certain data as to the character of the original.

[681]SeeRep. Brit. Assoc.1841, pp. 168, et seq.[682]SeeRep. Brit. Assoc.1841. pp. 160 and 169.[683]Some of the most beautiful of these almost perfect specimens have lately been figured and described by Prof. Owen in his Monograph on the Fossil Chelonian Reptiles of the Wealden and the Purbeck; Palæontographical Society, 1853.[684]Rep. Brit. Assoc. 1841, p. 177, and Monograph on Fossil Reptiles, Pal. Soc. 1849, in which the anatomical details are given with the characteristic accuracy and minuteness of the author.

[681]SeeRep. Brit. Assoc.1841, pp. 168, et seq.

[682]SeeRep. Brit. Assoc.1841. pp. 160 and 169.

[683]Some of the most beautiful of these almost perfect specimens have lately been figured and described by Prof. Owen in his Monograph on the Fossil Chelonian Reptiles of the Wealden and the Purbeck; Palæontographical Society, 1853.

[684]Rep. Brit. Assoc. 1841, p. 177, and Monograph on Fossil Reptiles, Pal. Soc. 1849, in which the anatomical details are given with the characteristic accuracy and minuteness of the author.

The Tertiary formations of India, however, have furnished decided examples of fossil terrestrial tortoises; and among the innumerable relics of the beings of an earlier world, which the indefatigable labours of Dr. Falconer and Captain Cautley have brought to light, and which those accomplished naturalists have so skilfully developed, are theremains of land tortoises of prodigious magnitude (Colossochelys atlas); one specimen indicating a length of twelve or fourteen feet, with a breadth and height of corresponding proportions! These remains are associated with the bones gigantic extinct mammalia, allied to thePalæotheriaand other pachyderms of the eocene deposits of the Paris basin; and with those of Emydian and Crocodilian reptiles.[685]

[685]Petrif.pp. 11 and 468.

Fossil Marine Turtles.—In illustration of this subject, I select a specimen discovered in the lower Chalk, at Burham, Kent, which is remarkable for its beautiful state of preservation, and its peculiar osteological characters.

Lign. 238. Chelone Benstedi:nat. size.Chalk. Kent.The dorsal shield or carapace of this specimen admits of being removed; and four sternal plates, a coracoid-bone, and several vertebræ are then exposed.

Chelone Benstedi.Lign.238.—To Mr. Bensted, of Maidstone, whose discoveries have rendered his quarry of Kentish Bag classic ground to the British palæontologist, I am indebted for this splendid fossil turtle. The quarry whence it was obtained is situated at Burham, a short distance from the banks of the Medway, between Chatham and Maidstone, and presents a good section of the lower Chalk. This locality is rich in fossil remains, rivalling in this respect the quarries near Lewes, Worthing, and Arundel, in Sussex. Two other fossil Turtles have been obtained from this quarry, and now enrich the cabinets of Sir P. Egerton and Mr. Bowerbank. Other relics of Chelonians found in this place are four marginal plates of the carapace, and fragments of ribs,[686]some marginal plates of a much larger individual, mandibles, and other fragments, which are noticed in Prof. Owen’s Monograph, 1851. The specimen, of whichLign.238is a reduced figure, consists of the dorsal buckler or carapace almost entire; it is of a depressed elliptical form, with a longitudinal median ridge; it is six inches in length, and three and a half inches in breadth across the middle. It is composed of eight ribs, or costal plates, on each side the dorsal ridge, which is formed of ten neural plates; andthere is a border of marginal plates. These plates are united to each other by finely indented sutures, and bear the imprints of the horny scutes, or tortoise-shell, with which they were originally invested. The expanded ribs are united throughout the proximal half of their length, and gradually taper to their marginal extremities, which are supported by the plates of the osseous border.[687]This description applies to the specimen as seen inLign.238; but Mr. Bensted soskilfully cleared away the chalk as to admit of the removal of a great part of the dorsal shield, by which means some of the vertebræ, four sternal (hyosternalandhyposternal) plates, and one of the coracoid bones are displayed. This brief description will suffice to convey a general idea of the characters of this fossil, which differs from any known recent turtle, and possesses some anomalous features, that appear to indicate some slight Emydian affinities.

[686]SeeGeol. Proceed, vol. iii. p. 299.[687]See alsoPhil. Trans.1841, p. 153, pl. xi. and xii.; andPalæontograph. Monograph, 1851, p. 4, plates i. ii. and iii.

[686]SeeGeol. Proceed, vol. iii. p. 299.

[687]See alsoPhil. Trans.1841, p. 153, pl. xi. and xii.; andPalæontograph. Monograph, 1851, p. 4, plates i. ii. and iii.

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 asChelone 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 inFoss. Til. For.pl. vi. and vii. Some examples must have belonged to an individual at least three feet in length. Unfortunately, thespecimens 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, figuredLign.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 extinctChelonewas 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 theMonograph,Weald. Rept.1853, this determination has lately been overlooked; and the specimen figuredTilg. Foss.pl. vi.fig.2, is referred to the newly namedCh. 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.

Fossil fresh-water Tortoises.—The remains of fresh-water Tortoises, referable to theEmydidæ, occur in the Purbeck and Wealden strata (Owen’sMonograph, 1853, andRep. Brit. Assoc.1841); the resemblance of some of these to the Jurassic species from Soleure was noticed by Cuvier (Oss. Foss.vol. v.). Among the Chelonian remains of the Wealden, some of the most remarkable are the costal plates and other bones of a Tortoise, which in its essential characters is closely allied to the Trionyces,[689]but differs from the recent forms, in having possessed a dermal horny integument, formed of scutes of tortoise-shell. The chelonians of the genus Trionyx (so named from their having three claws) have the extremities of the ribs free, and not articulated to a border of marginal plates, and there are intervals between their costal plates even in the adult state. The external surface of the bones of the buckler is covered with granulations, or with little pits, for the attachment of the soft skin, the only integument with which these animals are invested; and, being destitute of horny scutes, their bones exhibit no furrows, as in the other genera. But the fossil rib-plates (seeLign.241) have a shagreen-like or punctated surface, like the recent Trionyces, and at the same time bear the imprints of horny scutes; and, instead of being nearly of an equal width throughout their entire length, as in the existing species, have one extremity much wider than the other, as in the land-tortoises. From the slight degree of convexity of the ribs, it is evident that the carapace was much flattened, as in the Trionyx.[690]Except in having adefensive dermal integument, and agreeing in this respect with many of the Crocodilian reptiles, with which its bones are associated, the original must have closely resembled the existing predaceous fresh-water soft Turtles; and, doubtless, like those reptiles, inhabited the muddy beds of lakes and rivers, preying upon the eggs and young of the larger reptiles, and on the uniones and other fluviatile mollusca, whose shells are very commonly found imbedded with its remains.

[689]The relations of these peculiar remains toTrionyxwere pointed out inFoss. S. D.1822, p. 47.[690]SeePetrif.p. 157, &c.

[689]The relations of these peculiar remains toTrionyxwere pointed out inFoss. S. D.1822, p. 47.

[690]SeePetrif.p. 157, &c.

Lign. 241. Tretosternon Bakewelli;[691]1/3nat. size.Wealden.Tilgate Forest.(Foss. Tilg. For.pl. vi.fig.1.)One of the costal plates.

[691]This Tortoise, with the sanction of Baron Cuvier, was described under the nameTrionyx, inFoss. Tilg. For.1827, p. 60, and its distinctive characters were pointed out. InGeol. S. E.1833, p. 255, the specific nameBakewelliwas proposed in honour of the lateRobert Bakewell, Esq., whose excellent works have so greatly promoted the advancement of geology; a privilege to which, as the original discoverer of the species, and of its zoological relations, I was fairly entitled. But this name does not appear in the list of British Chelonians, either inRep. Brit. Assoc.1841, or in Mr. Morris’sCat. Brit. Org. Rem.1843. With a melancholy pleasure I now restore the name of my lamented friend, as a just, but very inadequate tribute of respect to his memory.

Lign. 242. Palæophis toliapicus:2/3nat. size.London Clay. Isle of Sheppey.Six concavo-convex vertebræ of the trunk.

FOSSIL SERPENTS.

VII. Ophidians, or Serpents.Lign.242.—The remains of the vertebral columns of extinct Serpents were discovered many years since in the London clay of the Isle of Sheppey, and specimens were obtained by the celebratedHunter, and preserved in his museum. These specimens, together with others in the collections of Messrs. Saull, Bowerbank, Dixon, Combe, and S. Wood, have been figured and described, and their relations to existing types elaborately worked out, by Professor Owen.[692]ThePalæophis typhæus, from the Bracklesham clay, had a length of about twenty feet, and, from the compressed character of its caudal vertebræ, was probably a sea-serpent. A somewhat smaller species also occurs at Bracklesham. The Sheppey specimens are referred to another species of this extinct genus, namely, theP. toliapicus(Lign.242); it was from ten to twelve feet in length. The remains of two species of land-serpents, respectively about four and three feet long, have been found at Hordwell Cliff. These belong to the extinct genusPaleryx, thus named in reference to the near affinities ofthe Hordwell vertebræ to those of the recentEryx, one of the Boa and Python group of serpents.[693]

[692]Geol. Trans. 2d ser. vol. vi. p. 209, &c. pl. xxii.; Rep. Brit. Assoc. 1841, p. 180; "Dixon’s Geology and Fossils of Sussex," pp. 211-217, pl. xii.fig.14; and especially Palæontographical Monograph, 1850, p. 51,et seq.; and plates xii. to xvi.[693]See Monograph on Eocene Reptiles, 1850, from which these notices of the Eocene Ophidians are abridged.

[693]See Monograph on Eocene Reptiles, 1850, from which these notices of the Eocene Ophidians are abridged.

The vertebræ of Serpents are distinguished by a transversely oblong anterior concavity, forming a deep cup, and a corresponding posterior convexity or hall; by the interlocking of the projecting posterior oblique processes with the anterior pair; and by the oblong tubercle on each side of the anterior part of the body of the vertebra, for moveable articulation with the head of the ribs; a spinal column thus constructed combines in the highest degree perfect flexibility with great strength.

In addition to the ophidian relics above referred to, fossil vertebræ of a small serpent (Palæophis?) have been found in the Eocene sand below the Bed Crag, at Kyson in Suffolk;[694]a locality that has yielded other organic remains of great interest (see chap. xix.; andWond.p. 258). The only fossils of this order of reptiles known to Baron Cuvier appear to have been some vertebræ from the bone-breccia of Cette (Oss. Foss.tom. iv. p. 177).

[694]Rep. Brit. Assoc. 1841, p. 181; and Monograph, 1850, p. 66.

Fossil eggs of snakes are occasionally met with in a comparatively recent limestone, of fresh-water origin, in Germany, near Offenbach, associated with shells of land and fresh-water molluscs. Like the turtles’ eggs on the shores of Ascension Island, these ova were probably laid in the moist mud, and became encrusted and preserved by a deposit of tufa.[695]

[695]Quart. Journ. Geol. Soc. vol. vi. part 2, p. 42.

BATRACHIANS.

VIII. Batrachians.—The reptiles termedBatrachians(from the Greek name for Frog) are characterized by the metamorphoses which they undergo in the progress of their development from the young to the adult state; the Frog,Toad, and Newt are familiar examples of this order. Their organs of aërial respiration consist of a pair of lungs; but in their young state they are provided with gills, supported, as in fishes, by cartilaginous arches. These organs disappear, in most species, when the animals arrive at maturity; but in a few genera, as the Siren and Proteus, they are persistent. The skeletons of these reptiles present corresponding modifications. The skull is, for the most part, much depressed, and the cerebral cavity small; it is united to the vertebral column by two distinct condyles, situated on the sides of the occipital or cranio-spinal aperture.[696]The vertebral column, in some genera (as, for example, in the common frog), is very short, and is reduced to eight or ten bones, the caudal vertebræ being fused into a long cylindrical style; but in the higher organised Batrachians the spine is composed of concavo-convex vertebræ, as in the Crocodile: in the lower type, as the Siren, Proteus, and Axolotl, the vertebræ are biconcave, as in numerous species of fossil Saurians. The ribs are merely rudimentary, being very short and few; a condition which has relation to the mode of reproduction in these animals, the eggs being accumulated and shed at once.[697]Some of the Batrachians are edentulous, but others have numerous small, conical, uniform, closely-arranged teeth, placed either in a single row, or aggregated like the rasp-teeth in fishes.[698]

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