THE Megalosaurus, as its name implies, was a Lizard, of great size, of which, although no skeleton has yet been found entire, so many perfect bones and teeth have been discovered in the same quarries, that we are nearly as well acquainted with the form and dimensions of its limbs, as if they had been found together in a single block of stone.*

From the size and proportions of these bones, as compared with existing Lizards, Cuvier concludes the Megalosaurus to have been an enormous reptile, measuring from forty to fifty feet in length, and partaking of the structure of the Crocodile and the Monitor.

* This genus was established by the Author, in a Memoir, published in the Geol. Trans. of London, (Vol. I., N. S. Pt. 2, 1824), and was founded upon specimens discovered in the oolitic slate of Stonesfield, near Oxford, the place in which these bones have as yet chiefly occurred. Mr. Mantell has discovered remains of the same animal in the Wealden fresh-water formation of Tilgate Forest; and from this circumstance we infer that it existed during the deposition of the entire series of oolitic strata. The author, in 1826, saw fragments of a jaw, containing teeth, and of some other bones of Megalosaurus, in the museum at Besançon, from the oolite of that neighbourhood.

[235 MEGALOSAURUS.] As the femur and tibia measure nearly three feet each, the entire hind leg must have attained a length of nearly two yards: a metatarsal bone, thirteen inches long, indicates a corresponding length in the foot.* The bones of the thigh and leg are not solid at the centre, as in Crocodiles, and other aquatic quadrupeds, but have large medullary cavities, like the bones of terrestrial animals. We learn from this circumstance, added to the character of the foot, that the Megalosaurus lived chiefly upon the land.

In the internal condition of these fossil bones, we see the same adaptation of the skeleton to its proper element, which now distinguishes the bones of terrestrial, from those of aquatic Saurians. In the Ichthyosauri and Plesiosauri, whose paddles were calculated exclusively to move in water, even the largest bones of the arms and legs were solid throughout. Their weight would in no way have embarrassed their action in the fluid medium they inhabited; but in the huge Megalosaurus, and still more gigantic Iguanodon, which are shown by the character of their feet to have been fitted to move on land, the larger bones of the legs were diminished

* See Geol. Trans. 2nd series, Vol. 3, p. 427, Pl. 41.

I learn from Mr. Owen that the long bones of land Tor toises have a close cancellous internal structure, but not a medullary cavity.

[236 GIGANTIC TERRESTRIAL SAURIANS.] in weight, by being internally hollow, and having their cavities filled with the light material of marrow, while their cylindrical form tended also to combine this lightness with strength.*

The form of the teeth shows the Megalosaurus

* The medullary cavities in the fossil bones of Megalosaurus, from Stonesfield, are usually filled with calcareous spar. In the Oxford Museum there is a specimen from the Wealden fresh water formation at Langton, near Tunbridge Wells, which is perhaps unique amongst organic remains: it presents the curious fact of a perfect cast of the interior of a large bone, apparently the femur of a Megalosaurus, exhibiting the exact form and ramifications of the marrow, whilst the bone itself has entirely perished. The substance of this cast is fine sand, cemented by oxide of iron, and its form distinctly represents all the minute reticulations, with which the marrow filled the intercolumniations of the cancelli, near the extremity of the bone. It exhibits also casts of the perforations along the internal parietes, whereby the vessels entered obliquely from the exterior of the bone, to communicate with the marrow. A mould of the exterior of the same bone has been also formed by the sandstone in which it was imbedded: hence, although the bone itself has perished, we have precise representations both of its external form and internal cavities, and a model of the marrow that filled this femur, nearly as perfect as could be made by pouring wax into an empty marrow-bone, and corroding away the bone with acid. The sand which formed this cast must have entered the medullary cavity by a fracture across the other extremity of the bone, which was wanting in the specimen.

From this natural preparation of ancient anatomy we learn that the disposition of marrow, and its connection with the reticulated extremities of the interior of the femur, were the same in these gigantic Lizards of a former world, as in medullary cavities of existing species.

[237 MEGALOSAURUS.] to have been in a high degree carnivorous: it probably fed on smaller reptiles, such as Crocodiles and Tortoises, whose remains abound in the same strata with its bones. It may also have taken to the water in pursuit of Plesiosauri and fishes.*

The most important part of the Megalosaurus yet found, consists of a fragment of the lower jaw, containing many teeth, (Pl. 23, Figs. 1'-2'). The form of this jaw shows that the head was terminated by a straight and narrow snout, compressed laterally like that of the Delphinus Gangeticus.

As in all animals, the jaws and teeth form the most characteristic parts, I shall limit my present observations to a few striking circumstances in the dentition of the Megalosaurus. From these we learn that the animal was a reptile, closely allied to some of our modern Lizards; and viewing the teeth as instruments for providing food to a carnivorous creature of enormous magnitude, they appear to have been admirably adapted to the destructive office for which they were designed. Their form and

* Mr. Broderip informs me that a living Iguana (I. Tuberculata), in the gardens of the Zoological Society of London, in the summer of 1834, was observed frequently to enter the water, and swim across a small pond, using its long tail as the instrument of progression, and keeping its fore feet motionless.

[238 GIGANTIC TERRESTRIAL SAURIANS.] mechanism will best be explained by reference to the figures in Pl. 23.*

In the structure of these teeth, (Pl. 23, Figs. 1, 2, 3), we find a combination of mechanical contrivances analogous to those which are adopted in the construction of the knife, the sabre, and the saw. When first protruded above the gum, (Pl. 23, Figs. 1'. 2'.) the apex of each tooth presented a double cutting edge of serrated enamel. In this stage, its position and line of action were nearly vertical, and its form like that of the two-edged point of a sabre, cutting equally on each side. As the tooth advanced in growth, it became curved

* The outer margin of the jaw (Pl. 23, Fig. 1'. 2'.) rises nearly an inch above its inner margin, forming a continuous lateral parapet to support the teeth on the exterior side, where the greatest support was necessary; whilst the inner margin (Pl.23, Fig. 1') throws up a series of triangular plates of bone, forming a zig-zag buttress along the interior of the alveoli. From tbe centre of each triangular plate, a bony partition crosses to the outer parapet, thus completing the successive alveoli. The new teeth are seen in the angle between each triangular plate, rising in reserve to supply the loss of the older teeth, as often as progressive growth, or accidental fracture, may render such renewal necessary; and thus affording an exuberant provision for a rapid succession and restoration of these most essential implements. They were formed in distinct cavities, by the side of the old teeth, towards the interior surface of the jaw, and probably expelled them by the usual process of pressure and absorption; insinuating themselves into the cavities thus left vacant. This contrivance for the renewal of teeth is strictly analogous to that which takes place in the dentition of many species of existing Lizards.

[239 MEGALOSAURUS.] backwards, in the form of a pruning knife, (Pl. 23, Figs. l. 2. 3,), and the edge of serrated enamel was continued downwards to the base of the inner and cutting side of the tooth, (Fig. 1, B. D.), whilst, on the outer side, a similar edge descended, but to a short distance from the point (Fig. 1, B. to C.), and the convex portion of the tooth (A.) became blunt and thick, as the back of a knife is made thick, for the purpose of producing strength . The strength of the tooth was further increased by the expansion of its sides, (as represented in the transverse section, Fig. 4, A. D). Had the serrature continued along the whole of the blunt and convex portion of the tooth, it would, in this position, have possessed no useful cutting power; it ceased precisely at the point (C.), beyond which it could no longer be effective. In a tooth thus formed for cutting along its concave edge, each movement of the jaw combined the power of the knife and saw; whilst the apex, in making the first incision, acted like the two-edged point of a sabre. The backward curvature of the full-grown teeth, enabled them to retain, like barbs, the prey which they had penetrated. In these adaptations, we see contrivances, which human ingenuity has also adopted, in the preparation of various instru ments of art.

In a former chapter (Ch. XIII.) I endeavoured

[240 GIGANTIC TERRESTRIAL SAURIANS.] to show that the establishment of carnivorous races throughout the animal kingdom tends materially to diminish the aggregate amount of animal suffering. The provision of teeth and jaws, adapted to effect the work of death most speedily, is highly subsidiary to the accomplishment of this desirable end. We act ourselves on this conviction, under the impulse of pure humanity, when we provide the most efficient instruments to produce the instantaneous, and most easy death, of the innumerable animals that are daily slaughtered for the supply of human food.
 
 

As the reptiles hitherto considered appear from their teeth to have been carnivorous, so we find extinct species of the same great family, that assumed the character and office of herbivora. For our knowledge of this genus, we are indebted to the scientific researches of Mr. Mantell. This indefatigable historian of the Wealden fresh-water formation, has not only found

[241 IGUANODON. HYLÆOSAURUS.] the remains of the Plesiosaurus, Megalosaurus, Hylæosaurus,* and several species of Crocodiles and Tortoises in these deposits, of a period intermediate between the oolitic and cretaceous series, but has also discovered in Tilgate Forest the remains of the Iguanodon, a reptile much more gigantic than the Megalosaurus, and which, from the character of its teeth, appears to have been herbivorous. The teeth of the Iguanodon are so precisely similar, in the principles of their construction, to the teeth of the modern Iguana, as to leave no

* The Hylæosaurus, or Lizard of the Weald, was discovered in Tilgate Forest, in Sussex, in 1832. This extraordinary Lizard was probably about twenty-five feet long. Its most peculiar character consists in the remains of a series of long, flat, and pointed bones, which seems to have formed an enormous dermal fringe, like the horny spines on the back of the modern Iguana. These bones vary in length from five to seventeen inches, and in width from three to seven inches and a half at the base. Together with them were found the remains of large dermal bones, or thick scales, which were probably lodged in the skin.

The Iguanodon has hitherto been found only, with one exception, in the Wealden fresh-water formation of the south of England, (Pl. 1, sec. 22.), intermediate between the marine oolitic deposits of the Portland stone and those of the green- sand formation in the cretaceous series. The discovery, in 1834, (Phil. Mag. July 1834, p. 77), of a large proportion of the skeleton of one of these animals, in strata of the latter formation, in the quarries of Kentish Rag, near Maidstone, shews that the duration of this animal did not cease with the completion of the Wealden series. The individual from which this skeleton was derived had probably been drifted to sea, as those which afforded the bones found in the fresh-water deposits

[242 GIGANTIC TERRESTRIAL SAURIANS.] doubt of the near connection of this most gigantic extinct reptile with the Iguanas of our own time. When we consider that the largest living Iguana rarely exceeds five feet in length, whilst the congenerous fossil animal must have been nearly twelve times as long, we cannot but be impressed by the discovery of a resemblance, amounting almost to identity, between such characteristic organs as the teeth, in one of the most enormous among the extinct reptiles of the fossil world, and those of a genus whose largest species is comparatively so diminutive.

According to Cuvier, the common Iguana inhabits all the warm regions of America: it lives chiefly upon trees, eating fruits, and seeds, and leaves. The female occasionally visits the water, for the purpose of laying in the sand its eggs, which are about the size of those of a pigeon. *

subjacent to this marine formation, had been drifted into an estuary. This unique skeleton is now in the museum of Mr. Mantell, and confirms nearly all his conjectures respecting the many insulated bones which he had referred to the Iguanodon.

* In the Appendix to a paper in the Geol. Trans. Lond. (N. S. Vol. III. Pt. 3) on the fossil bones of the Iguanodon, found in the Isle of Wight and Isle of Purbeck, I have mentioned the following facts, illustrative of the herbivorous habits of the living Iguana.

In the spring of 1829, " Mr. W. J. Broderip saw a living Iguana, about two feet long, in a hothouse at Mr. Miller's nursery gardens, near Bristol. It had refused to eat insects, and

[243 IGUANODON.] As the modern Iguana is found only in the warmest regions of the present earth, we may reasonably infer that a similar, if not a still warmer climate, prevailed at the time when so huge a Lizard as the Iguanodon inhabited what are now the temperate regions of the southern coasts of England. We know from the fragment of a femur in the collection of Mr. Mantell, that the thigh-bone of this reptile much exceeded in bulk that of the largest Elephant: this fragment presents a circumference of twenty-two inches in its smallest part, and the entire length must have been between four and five feet. Comparing the proportions of this monstrous bone with those of the fossil teeth with which it is associated, it appears that they bear to one another nearly the same ratio that the femur of the Iguana bears to the similarly constructed and peculiar teeth of that animal.*

other kinds of animal food, until happening to be near some kidney-bean plants that were in the house for forcing, it began to eat of their leaves, and was from that time forth supplied from these plants." In 1828, Captain Belcher found, in the island of Isabella, swarms of Iguanas, that appeared omnivorous; they fed voraciously on the eggs of birds, and the intestines of fowls and insects.

From a careful comparison of t.he bones of the Iguanodon with those of the Iguana, made by taking an average from the proportions of different bones from eight separate parts of the respective skeletons, Mr. Mantell has arrived at these dimensions as being the propotionate measures of the following parts of this extraordinary reptile:

244 GIGANTIC TERRESTRIAL SAURIANS.

It has been stated, in the preceding section, that the large medullary cavities in the femur of the Iguanodon, and the form of the bones of the feet, show that this animal, like the Megalosaurus, was constructed to move on land.

A further analogy between the extinct fossil and the recent Iguana is offered by the presence in both of a horn of bone upon the nose, (Pl. 24, Fig. 14). The concurrence of peculiarities so remarkable as the union of this nasal horn with a mode of dentition of which there is no example, except in the Iguanas, affords one of the many proofs of the universality of the laws of co-existence, which prevailed no less constantly throughout the extinct genera and species of the fossil world, than they do among the living members of the animal kingdom.

 
 

	Feet.
Length from snout to the extremity of the tail.	70
Length of tail.	52 1/2
Circumference of body.	14 1/2

Mr. Mantell calculates the femur of the Iguanodon to be twenty times the size of that of a modern Iguana; but as animals do not increase in length in the same ratio as in bulk, it does not follow that the Iguanodon attained the enormous length of one hundred feet, although it approached perhaps nearly to seventy feet.

As the Iguanodon, from its enormous bulk, must have been unable to mount on trees, it could not have applied its tail to the same purpose as the Iguana, to assist in climbing; and the longitudinal diameter of its caudal vertebrae is much less in proportion than in the Iguana, and shows the entire tail to have been comparatively shorter.

[245 IGUANODON.]

As the teeth are the most characteristic and important parts of the animal, I shall endeavour to extract from them evidence of design, both in their construction and mode of renewal, and also in their adaptation to the office of consuming vegetables, in a manner peculiar to themselves. They are not lodged in distinct sockets, like the teeth of Crocodiles, but fixed, as in Lizards, along the internal face of the dental bone, to which they adhere by one side of the bony substance of their root. (Pl. 24, Fig. 13.)

The teeth of most herbivorous quadrupeds, (exclusively of the defensive tusks), are divided into two classes of distinct office, viz, incisors and molars; the former destined to collect and sever vegetable substances from the ground, or from the parent plant; the latter to grind and masticate them on their way towards the stomach. The living Iguanas, which are in great part herbivorous, afford a striking exception to this economy: as their teeth are little fitted for grinding, they transmit their food very slightly comminuted into the stomach.

Our giant Iguanodon, also, had teeth resembling those of the Iguana, and of so herbivorous a character, that at first sight they were supposed by Cuvier to be the teeth of a Rhinoceros.

[246 GIGANTIC TERRESTRIAL SAURIANS.] The examination of these teeth will lead us to the discovery of remarkable contrivances, adapting them to the function of cropping tough vegetable food, such as the Clathraria, and similar
plants, which are found buried writh the Iguanodon, might have afforded. We know the form and power of iron pincers to gripe and tear nails from their lodgment in wood: a still more powerful kind of pincers, or nippers, is constructed for the purpose of cutting wire, which yields to them nearly as readily as thread to a pair of scissors. Our figures (Pl. 24, Figs. 6, 7, 8, 12) show the place of the cutting edges, and form of curvature, and points of enlargement and contraction, in the teeth of the Iguanodon, to be nearly the same as in the corresponding parts of these powerful metallic tools; and the mechanical advantages of such teeth, as instruments for tearing and cuttIng, must have been similar.*

The teeth exhibit also two kinds of provisions to maintain sharp edges along the cutting surface, from their first protrusion, until they were worn down to the very stump. The first

* Fig. 2. represents the front of a young tooth ; and Figs. 5, 6, 7, 8, the front of four other teeth, thrown slightly into profile. In all of these we recognise a near approach to the form of the nipping pincers, with a sharp cutting edge at the upper margin of the enamel. The enamel is here expressed by wavy lines, which represent its actual structure : it is placed only in front, like the enamel in front of the incisors of Rodentia.

[247 IGUANODON.] of these is a sharp and serrated edge, extending on each side downwards, from the point to the broadest portion of the body of the tooth. (See Figs. 1, 2, 6, 8, 12, &c.)

The second provision is one of compensation for the gradual destruction of this serrated edge, by substituting a plate of thin enamel, to maintain a cutting power in the anterior portion of the tooth, until its entire substance was consumed in service.*

Whilst the crown of the tooth was thus gradually diminishing above, a simultaneous absorption of the root went on below, caused by the pressure of a new tooth rising to replace the old one, until by this continual consumption at both extremities, the middle portion of the older tooth was reduced to a hollow stump, (Figs. 10, 11), which fell from the jaw to make room for a

* This perpetual edge resulted from the enamel being placed only on the front of the tooth, like that on the incisors of Rodentia. As the softer material of the tooth itself must have worn away more readily than this enamel, and most readily at the part remotest from it, an oblique section of t.he crown was thus perpe tually maintained, with a sharp cutting edge in front, like that of the nippers. (See Figs. 7. 8. 12.)

The younger tooth, (Fig. 1), when first protruded, was lancet shaped, with a serrated edge, extending on each side downwards, from the point to its broadest portion, as in the living Iguana. (Pl. 24.f. 13, and Fig. 4.) This serrature ceased at the broadest diameter of the tooth, i. e. precisely at the line, below which, had they been continued, they would have had no effect in cutting. (Pl. 24. f. 2. 6. 8. 9. 12.) As these saws were gradually worn away, the cutting power was transferred to the enamel in front,

[248 GIGANTIC TERRESTRIAL SAURIANS.] more efficient successor.* In this last stage the form of the tooth had entirely changed, and the crown had become flat, like the crown of worn out human incisors, and capable of performing imperfect mastication after the cutting powers had diminished. There is, I believe, no other example of teeth which possess the same mechanical advantages as instruments of cutting and tearing portions of vegetable matter from tough and rigid plants. In this curious piece of animal mechanism, we find a varied adjustment of all parts and proportions of the tooth, to the exercise of peculiar functions; attended by compensations adapted to shifting conditions of the instrument, during different stages of its

and here we find a provision of another kind to give efficacy and strength. The front was traversed longitudinally by alternate ridges and furrows, (Pl. 24, Figs. 2, 5, 6, 7, 8), the ridges serving as ribs or buttresses to strengthen and prevent the enamel from scaling off, and forming, together with the furrows, an edge slightly wavy, and disposed in a series of minute gouges, or fluted chisels; hence the tooth became an instrument of greater power to cut tough vegetables under the action of the jaw, than if the enamel had been in a continuous straight line. By these contrivances, also it continued effective during every stage through which it passed, from the serrated lancet-point of the new tooth, (Fig. 1), to its final consumption. (Fig. 10, 11.)

* In Pl. 24, Fig. 13, the jaw of a recent Iguana exhibits the commencement of this process, and a number of young teeth are seen forcing their way upwards, and causing absorption at the base of the older teeth. Figs. 10, 11, exhibit the effect of similar absorption upon the residuary stump of the fossil tooth of an Iguanodon.

[249 IGUANODON.] consumption. And we must estimate the works of nature by a different standard from that which we apply to the productions of human art, if we can view such examples of mechanical contrivance, united with so much economy of expenditure, and with such anticipated adaptations to varying conditions in their application, without feeling a profound conviction that all this adjustment has resulted from design and high intelligence.
 
 

THE fossil reptiles of the Crocodilean family do not deviate sufficiently from living genera, to require any description of peculiar and discontinued contrivances, like those we have seen in the Ichthyosaurus, Plesiosaurus, and Pterodactyle; but their occurrence in a fossil state is of high importance, as it shows that whilst many forms of vertebrated animals have one after another been created, and become extinct, during the successive geological changes of the surface of our globe; there are others which have survived

[250 AMPHIBIOUS SAURIANS.]  all these changes and revolutions, and still retain the leading features under which they first appeared upon our planet.

If we look to the state of the earth, and the character of its population, at the time when Crocodilean forms were first added to the number of its inhabitants, we find that the highest class of living beings were reptiles, and that the only other vertebrated animals which then existed were fishes; the carnivorous reptiles at this early period must therefore have fed chiefly upon them, and if in the existing family of Crocodiles there be any, that are in a peculiar degree piscivorous, their form is that we should expect to find in those most ancient fossil genera, whose chief supply of food must have been derived from fishes.

In the living sub-genera of the Crocodilean family, we see the elongated and slender beak of the Gavial of the Ganges, constructed to feed on fishes; whilst the shorter and stronger snout of the broad-nosed Crocodiles and Alligators gives them the power of seizing and devouring quadrupeds, that come to the banks of rivers in hot countries to drink. As there were scarcely any mammalia* during the secondary periods, whilst the waters were abundantly stored with

* The small Opossums in the oolite formation at Stonesfield, near Oxford, are the only land mammalia whose bones have been yet discovered in any strata more ancient than the tertiary.

[251 CROCODILEANS.] fishes, we might, a priori, expect that if any Crocodilean forms had then existed they would most nearly have resembled the modern Gavial. And we have hitherto found only those genera which have elongated beaks, in formations anterior to, and including the chalk; whilst true Crocodiles, with a short and broad snout, like that of the Cayman and the Alligator, appear for the first time in strata of the tertiary periods, in which the remains of inammalia abound.*

During these grand periods of lacustrine mammahia, in which but few of the present genera of terrestrial carnivora had been called into existence, the important office of controlling the excessive increase of the aquatic herbivora appears to have been consigned to the Crocodiles, whose habits fitted them, in a peculiar degree, for such a service. Thus, the past history of the Crocodilean tribe presents another example of the well regulated workings of a

* One of these, found by Mr. Spencer in the London clay of the Isle of Sheppy, is engraved, Pl. 25', Fig. l. Crocodiles of this kind have been found in the chalk of Meudon, in the plastic clay of Auteuil, hi the London clay, in the gypsum of Mont Martre, and in the lignites of Provence.

The modern broad-nosed Crocodileans, though they have the power to capture mammalia, are not limited to this kind of prey; they feed largely also on fishes, and occasionally on birds. This omnivorous character of the existing Crocodilean family, seems adapted to the present general diffusion of more varied kinds of food, than existed when the only form of the beak in this family was fitted, like that of the Gavial, to feed chiefly on fishes.

[252 AMPHIBIOUS SAURIANS.] consistent plan in the economy of animated nature, under which each individual, whilst following its own instinct, and pursuing its own good, is instrumental in promoting the general welfare of the whole family of its co-temporaries [sic].

Cuvier observes, that the presence of Crocodilean reptiles, which are usually inhabitants of fresh water, in various beds, loaded with the remains of other reptiles and shells that are decidedly marine, and the further fact of their being, in many cases, accompanied by fresh water Tortoises, shows that there must have existed dry land, watered by rivers, in the early periods when these strata were deposited, and long before the formation of the lacustrine tertiary strata of the neighbourhood of Paris.* The living species of the Crocodile family are twelve in number, namely, one Gavial, eight true Crocodiles, and three Alligators. There are also many fossil species: no less than six of these have been made out by Ctivier, and several

* M. Geoffroy St. Hilaire has arranged the fossil Saurians with long and narrow beaks, like that of the Gavial, under the two new genera, Teleosaurus and Steneosaurus. In the Teleosaurus, (Pl. 25'. Fig. 2.) the nostrils form almost a vertical section of the anterior extremity of the beak; in the Steneosaurus, (Pl. 25', Fig. 3.) this anterior termination of the nasal canal had nearly the same arrangement as in the Gavial, opening upwards, and being almost semi-circular on each side. — Recherches sur les grands Sauriens, 1831.

[253 CROCODILEANS.] others, from the secondary and tertiary formations in England remain to be described.*

It would be foreign to our present purpose, to enter into a minute comparison of the osteology of living and fossil genera and species of this family. We may simply observe, with respect to their similar manner of dentition, that they all present the same examples of provision for extraordinary expenditure of teeth, by an un usually abundant store of these most essential organs. As Crocodiles increase to no less than four hundred times their original bulk,

* One of the finest specimens of fossil Teleosauri yet discovered, (see Pl. 25, Fig. 1), was found in the year 1824, in the alum shale of the lias formation at Saltwick, near Whitby, and is engraved in Young and Bird's Geological Survey of the Yorkshire Coast, 2d Ed. 1828: its entire length is about eighteen feet, the breadth of the head twelve inches, the snout was long and slender, as in the Gavial, the teeth, one hundred and forty in number, are all small and slender, and placed in nearly a straight line. The heads of two other individuals of the same species, found near Whitby, are represented in the same plate, Figs. 2. 3.

Some of the ungual phalanges, which are preserved on the hind feet of this animal, Fig. 1, show that these extremities were terminated by long and sharp claws, adapted for motion upon land, from which we may infer that the animal was not exclusively marine; from the nature of the shells with which they are associated, in the lias and oolite formations, it is probable that both the Steneosaurus and Teleosaurus frequented shallow seas. Mr. Lyell states that the larger Alligator of the Ganges sometimes descends beyond the brackish water of the delta into the sea.

This mode of dentition has been already exemplified in speaking of the dentition of the Ichthyosaurus, P. 172, and Pl. 11. A.

[254 AMPHIBIOUS SAURIANS.] between the period at which they leave the egg and their full maturity, they are provided with a more frequent succession of teeth than the mammalia, in order to maintain a duly proportioned supply during every period of their life. As the predaceous habits of these animals cause their teeth, placed in so long a jaw, to be peculiarly liable to destruction, the same provision serves also to renew the losses which must often be occasioned by accidental fracture.

The existence of these remedial forces, thus uniformly adapted to supply anticipated wants, and to repair foreseen injuries, affords an example of those supplementary contrivances, which give double strength to the argument from design, in proof of the agency of Intelligence, in the construction and renovation of the animal machinery in which such contrivances are introduced.

The discovery of Crocodilean forms so nearly allied to the living Gavial, in the same early strata that contain the first traces of the Ichthyosaurus and the Plesiosaurus, is a fact which seems wholly at variance with every theory that would derive the race of Crocodiles from Ichthy osauri and Plesiosauri, by any process of gradual transmutation or developement. The first appearance of all these three families of reptiles seems to have been nearly simultaneous; and they all continued to exist together until the

[255 FOSSIL TESTUDINATA.] termination of the secondary formations; when the Ichthyosauri and Plesiosauri became extinct, and forms of Crocodiles, approaching to the Cayrnan and the Alligator, were for the first time introduced.
 
 

AMONG the existing animal population of the warmer regions of the earth, there is an extensive order of reptiles, comprehended by Cuvier under the name of Chelonians, or Tortoises. These are subdivided into four distinct families; one inhabiting salt water, two others fresh water lakes and rivers, and a fourth living entirely upon the land. One of the most striking characters of this Order consists in the provision that is made for the defence of creatures, whose movements are usually slow and torpid, by in closing the body within a double shield or cuirass, formed by the expansion of the vertebræ, ribs and sternum, into a broad bony case.

The small European Tortoise, Testudo Græca, and the eatable Turtle, Chelonia Mydas, are familiar examples of this peculiar arrangement both in terrestrial and aquatic reptiles; in each

[256 FOSSIL TESTUDINATA.] case the shield affords compensation for the want of rapidity of motion to animals that have no ready means of escape by flight or concealment from their enemies. We learn from Geology that this Order began to exist nearly at the same time with the Order of Saurians, and has continued coextensively with them through the secondary and tertiary formations, unto the present time: their fossil remains present also the same threefold divisions that exist among modern Testudinata, into groups respectively adapted to live in salt and fresh water, and upon the land.

Animals of this Order have yet been found only in strata more recent than the carboniferous series.* The earliest example recorded by Cuvier, (Oss. Foss. Vol. 5, Pt. 2, p. 525), is that of a very large species of Sea Turtle, the shell of which was eight feet long, occurring in the Muschelkalk at Luneville. Another marine species has been found at Glaris, in slate referrible to the lower cretaceous formation. A third occurs in the upper cretaceous freestone at Maestricht. All these are associated with the remains of other animals that are marine; and though they differ both from living Turtles and from one another, they still exhibit such general accordance in

* The fragment from the Caithness slate, engraved in the Geol. Trans. Lond. V. iii. Pl. 16, Fig. 6, as portions of a trionyx, is pronounced by M. Agassiz to be part of a fish.

[257 TRIONYX EMYS.] the principles of their construction, with the conditions by which existing Turtles are fitted for their marine abode, that Cuvier was at once enabled to pronounce these fossil species to have been indubitably inhabitants of the sea.*

The genera Trionyx and Emys, present their fossil species in the Wealden freshwater formations of the Secondary series; and still more abundantly in the Tertiary lacustrine deposits; all these appear to have lived and died, under circumstances analogous to those which attend their cognate species in the lakes and rivers of the present tropics. They have also been found

* Plate 25'. Fig. 4, represents a Turtle from the slate of Glaris: it is shewn to have been marine by the unequal elongation of the toes in the anterior paddle; because, in freshwater Tortoises, all the toes are nearly equal, and of moderate length; and in land Tortoises, they are also nearly equal, and short; but in all marine species they are very long, and the central toe of the anterior paddle, is by much the longest of all. The accordance with this latter condition in the specimen before us, is at once apparent; and both in this respect and in general structure, it approaches very nearly to living genera. This figure is copied from Vol. 5, Pt. 2, Tab. 14, f. 4, of the Oss. Foss. of Cuvier. M. Agassiz has favoured me with the following details respecting important parts which are imperfectly represented in the drawing from which Cuvier's engraving was taken. "The ribs show evidently that it is nearly connected with the genera Chelonia and Sphargis, but referrible to no known species; the fingers of the left fore paddle are five in number; the two exterior are the shortest, and have each three articulations ; and the three internal fingers, of which the middle one is the longest, have each four articulations, as in the existing genera, Chelonia and Sphargis."

[258 FOSSIL TESTUDINATA.] in marine deposits, where their admixture with the remains of Crocodilean animals shows that they were probably drifted, together with them, into the sea, from land, at no great distance.*

In the close approximation of the generic characters of these fossil Testudinata, of various and ancient geological epochs, to those of the present day, we have a striking example of the unity of design which has pervaded the construction of animals, from the most distant periods in which these forms of organized beings were also called into existence. As the paddle of the Turtle has at all times been adapted to move in the waves of the sea, so have the feet of the Trionyx and Emys ever been constructed for a more quiescent life in freshwater, whilst those of the Tortoise have been no less uniformly fitted to creep and burrow upon land.

The remains of land Tortoises have been more rarely observed in a fossil state. Cuvier mentions but two examples, and these in very recent formations at Aix, and in the Isle of France.

Scotland has recently afforded evidence of the existence of more than one species of these

* Thus two large extinct species of Emys occur, together with
marine shells, in the jura limestone at Soleure. The Emys also and Crocodiles, are found in the marine deposits of the London clay at Sheppy and Harwich; and the former is associated with marine exuviæ at Brussels. Very perfect impressions of small horny scales of Testtidinata, occur in the Oolite slate of Stonesfield, near Oxford.

[259 LAND TORTOISES.] terrestrial reptiles, during the period of the New red, or Variegated sandstone formation. (See Pl. 1, Sec. 17). The nature of this evidence is almost unique in the history of organic remains.*

It is not uncommon to find on the surface of sandstone, tracks which mark the passage of small Crustacea and other marine animals, whilst

* See Dr. Duncan's account of tracks and footmarks of animals, impressed on sandstone in the quarry of Corn Cockle Muir, Dumfries-shire, Trans. Royal Society of Edinburgh, 1828.

Dr. Duncan states that the strata which bear these impressions lie on each other like volumes on the shelf of a library, when all inclining to one side: that the quarry has been worked to the depth of forty-five feet from the top of the rock; throughout the whole of this depth similar impressions have been found, not on a single stratum only, but on many successive strata; i. e. after removing a large slab which contained foot-prints, they found perhaps the very next stratum at the distance of a few feet, or it might be less than an inch, exhibiting a similar phenomenon. Hence it follows that the process by which the impressions were made on the sand, and subsequently buried, was repeated at successive intervals.

I learn, by a letter from Dr. Duncan, dated October, 1834, that similar impressions, attended by nearly the same circumstances, have recently been discovered about ten miles south of Corn Cockle Muir, in the Red sandstone quarries of Craigs, two miles east of the town of Dumfries. The inclination of the strata of this place is about 45° S.W. like that of almost all the sandstone strata of the neighbourhood. One of these tracks extended from twenty to thirty feet in length: in this place also, as at Corn Cockle Muir, no bones of any kind have yet been discovered.

Sir William Jardine has informed Dr. Duncan that tracks of animals have been found also in other quarries near Corn Cockle Muir.

260 RIPPLE MARKINGS.

this stone was in a state of loose sand at the bottom of the sea. Laminated sandstones are also often disposed in minute undulations, resembling those formed by the npple of agitated water upon sand.*

The same causes, which have so commonly preserved these undulations, would equally preserve any impressions that might happen to have been made on beds of sand, by the feet of animals; the only essential condition of such preservation being, that they should have become covered with a further deposit of earthy matter, before they were obliterated by any succeeding agitations of the water.

The nature of the impressions in Dumfries In 1831, Mr. G. P. Scrope, after visiting the quarries of
Dumfries-shire

found rippled markings, and abundant foot tracks of small animals on the Forest marble beds north of Bath. These were probably tracks of Crustacea. — See Phil. Mug. May, 1831, p. 376.

We find on the surface of slabs both of the calcareous grit, and Stonesfield slate, near Oxford, and on sandstones of the Wealden formation, in Sussex and Dorsetshire, perfectly preserved and petrified castings of marine worms, at the upper extrernity of holes bored by them in the sand, while it was yet soft at the bottom of the water; and within the sandstones, traces ,of tubular holes in which the worms resided. The preservation of these tubes and castings shews the very quiet condition of the bpttom, and the gentle action of the water, which brought the materials that covered them over, without disturbiiig them.

Cases of this kind add to the probability of the preservation of footsteps of Tortoises on the Red sandstone, and also afford proof of the alternation of intervals of repose with periods of violence, during the destructive processes by which derivative strata were formed.

[261 FOSSIL FOOTSTEPS.] may be seen by reference to Pl. 26. They traverse the rock in a direction either up or down, and not across the surfaces of the strata, which are now inclined at an angle of 38°. On one slab there are twenty-four continuous impressions of feet, forming a regular track, with six distinct repetitions of the mark of each foot, the fore-foot being differently shaped from the hind-foot; the marks of claws are also very distinct.*

Although these footsteps are thus abundant in the extensive quarries of Corn Cockle Muir, no trace whatever has been found of any portion of the bones of the animals whose feet they represent. This circumstance may perhaps be explained by the nature of the siliceous sandstone having been unfavourable to the preservation of organic remains. The conditions which would admit of the entire obliteration of bones,

* On comparing some of these impressions with the tracks which I caused to be made on soft sand, and clay, and upon unbaked pie-crust, by a living Emys and Testudo Græca, I found the correspondence with the latter sufficiently close, allowing for difference of species, to render it highly probable that the fossil footsteps were also impressed by the feet of land Tortoises.

In the bed of the Sapey and Whelpley brooks near Tenbury, circular markings occur in the Old Red Sandstone, which are referred by the natives to the tracks of Horses, and the impressions of Patten-rings, and a legendary tale has been applied to explain their history. They are caused by concretions of Marlstone and Iron, disposed in spherical cases around a solid core of sandstone, and intersected by these water courses.

[262 FOSSIL FOOTSTEPS.] would in no way interfere with the preservation of impressions made by feet, and speedily filled up by a succeeding deposit of sand, which would assume, with the fidelity of an artificial plaster mould, the precise form of the surface to which it was applied.

Notwithstanding this absence of bones from the rocks which are thus abundantly impressed with footsteps, the latter alone suffice to assure us both of the existence and character of the ani mals by which they were made. Their form is much too short for the feet of Crocodiles, or any other known Saurians; and it is to the Testudinata, or Tortoises, that we look, with most probability of finding the species to which their origin is due.*

The Historian or the Antiquary may have traversed the fields of ancient or of modern

* This evidence of footsteps, on which we are here arguing, is one which all mankind appeal to in every condition of society. The thief is identified by the impression which his shoe has left near the scene of his depredations. Captain Parry found the tracks of human feet upon the banks of the stream in Possession Bay, which appeared so fresh, that he at first imagined them to have been recently made by some natives: on examination they were distinctly ascertained to be the marks of the shoes of some of his own crew, eleven months before. The frozen condition of the soil had prevented their obliteration. The American savage not only identifies the Elk and Bison by the impression of their hoofs, but ascertains also the time that has elapsed since each animal had passed. From the Camel's track upon the sand, the Arab can determine whether it was heavily or lightly laden, or whether it was lame.

[263 FOSSIL FOOTSTEPS.] battles; and may have pursued the line of march of triumphant Conquerors, whose armies trampled down the most mighty kingdoms of the world. The winds and storms have utterly obliterated the ephemeral impressions of their course. Not a track remains of a single foot, or a single hoof, of all the countless millions of men and beasts whose progress spread desolation over the earth. But the Reptiles, that crawled upon the half-finished surface of our infant planet, have left memorials of their passage, enduring and indelible. No history has recorded their creation or destruction ; their very bones are found no more among the fossil relics of a former world. Centuries, and thousands of years, may have rolled away, between the time in which these footsteps were impressed by Tortoises upon the sands of their native Scotland, and the hour when they are again laid bare, and exposed to our curious and admiring eyes. Yet we behold them, stamped upon the rock, distinct as the track of the pass~ ing animal upon the recent snow; as if to show that thousands of years are but as nothing amidst Eternity — and, as it were, in mockery of the fleeting perishable course of the mightiest Potentates among mankind.*

A similar discovery of fossil footsteps has recently been made in Saxony, at the village of Hessberg, near Hildburg-hausen, in several quarries of grey quartzose sandstone, alternating

[264 FOSSIL FISHES.]

THE history of Fossil Fishes is the branch of Pakeontology which has hitherto received least attention, in consequence of the imperfect

with beds of red sandstone, nearly of the same age with that of Dumfries. (See Pl. 26'. 26". 26"'.)

The following account of them is collected from notices by Dr. Hohnbaum and Professor Kaup. "The impressions of feet are partly hollow, and partly in relief; all the depressions are upon the upper surfaces of slabs of sandstone, whilst the reliefs are only upon the lower surfaces, covering those which bear the depressions. These reliefs are natural casts, formed in the subjacent footsteps as in moulds. On one slab (see Pl. 26'), six feet long by five feet wide, there occur many footsteps of more than one animal, and of various sizes. The larger impressions, which seem to be of the hind foot, are eight inches long, and five wide. (See Pl. 26".) One was twelve inches long. Near to each large footstep, and at the regular distance of an inch and a half before it, is a smaller print of a fore-foot, four inches long and three inches wide. These foot steps follow one another in pairs, at intervals of fourteen inches from pair to pair, each pair being in the same line. Both large and small steps have the great toes alternately on the right and left side; each has the print of five toes, and the first, or great toe is bent inwards like a thumb. The fore and hind foot are nearly similar in form, though they differ so greatly in size.

On the same slabs are other tracks, of smaller and differently

[265 FOSSIL FISHES.] state of our knowledge of existing Fishes. The inaccessible recesses of the waters they inhabit, renders the study of their nature and habits much more difficult than that of terrestrial animals. The arrangement of this large and important class of Vertebrata was the last great work undertaken by Cuvier, not long before his lamented death, and nearly eight thousand species of living Fishes had come under his observation. The full development of their history

shaped feet, armed with nails. Many of these (Pl. 26') resemble the impressions on the sandstone of Dumfries, and are apparently the steps of Tortoises.

Professor Kaup has proposed the provisional name of Chirotherium for the great unknown animal that formed the larger footsteps, from the distant resemblance, both of the fore and hind feet, to the impression of a human hand; and he conjectures that they may have been derived from some quadruped allied to the Marsupialia. The presence of two small fossil mammalia related to the Opossum, in the Oolite formation of Stonesfield, and the approximation of this order to the class of Reptiles, which has already been alluded to, (page 73, note), are circumstances which give probability to such a conjecture. In the Kangaroo, the first toe of the fore-foot is set obliquely to the others, like a thumb, and the disproportion between the fore and hind feet is also very great.

A further account of these footsteps has been published by Dr. Sickler, in a letter to Blumenbach, 1834. Our figure (Pl. 26'), is copied from a plate that accompanies this letter; on comparing it with a large slab, covered with similar footmarks, from the same quarries, lately placed in the British Museum, (1835) I find that the representations, both of the large and small foot steps, correspond most accurately. The hind foot (Pl. 26"), is drawn from one on this slab. Pl. 26"' is drawn from a plaster

[266 FOSSIL FISHES.] and numbers, and of the functions they discharge in the economy of nature, he has left to his able successors.

The fact of the formation of so large a portion of the surface of the earth beneath the water, would lead us to expect traces of the former existence of Fishes, wherever we have the remains of aquatic Mollusca, Articulata, and Radiata. Although a few remarkable places have long been celebrated as the repositories of fossil Fishes, even of these there are some, whose geological relations have scarcely yet been ascertained, while the nature of their Fishes remains in still greater obscurity.*

The task of arranging all this disorder has

cast in the British Museum, taken from another slab found in the same quarries, and impressed with footsteps of some small aquatic Reptile.

Some fragments of bones were found in the same quarries with these footsteps, but were destroyed.

A thin deposit of Green Marl, which lay upon the inferior bed of sand, at the time when the footsteps were impressed, causes the slabs above and below it to part readily, and exhibit the casts that were formed by the upper sand, in the prints that the animals had made on the lower stratum, through the marl, while soft, and sufficiently tenacious to retain the form of the footsteps.

* The most celebrated deposits of fossil Fishes in Europe are the coal formation of Saarbrück, in Lorraine the bituminous slate of Mansfeld, in Thuringia; the calcareous lithographic slate of Solenhofen; the compact blue slate of Glaris; the limestone of Monte Bolca, near Verona; the marlstone of Oeningen, in Switzerland; and of Aix, in Provence.

Every attempt that has yet been made at a systematic arrangement

[266 MOST IMPORTANT TO GEOLOGY.] at length been undertaken by an individual, to whose hands Cuvier at once consigned the materials he had himself collected for this important work. The able researches of Professor Agassiz have already extended the number of fossil Fishes to two hundred genera, and more than eight hundred and fifty species.* The results of his enquiry throw a new and most important light on the state of the earth, during each of the great periods into which its past history has been divided. The study of fossil Ichthyology is therefore of peculiar importance to the geologist, as it enables him to follow an entire Class of animals, of so high a Division as the vertebrate, through the whole series of geological formations; and to institute comparisons between their various conditions during successive Periods of the earth's formation, such as Cuvier could carry only to a much more limited extent in the classes of Reptiles, Birds, and Mammifers, for want of adequate materials.

of these Fishes has been more or less defective, from an endeavour to arrange them under existing genera and families. The imperfection of his own, and of all preceding classifications of Fishes, is admitted by Cuvier; and one great proof of this imperfection is that they have led to no general results, either in Natural History, Physiology, or Geology.

* No existing genus is found among the fossil Fishes of any stratum older than the Chalk formation. In the inferior chalk there is one living genus, Fistularia ; in the true chalk, five; and in the Tertiary strata of M. Bolca, thirty-nine living genera, and thirty-eight which are e xtinct. — Agassiz.

[268 SYSTEM OF AGASSIZ.] The system upon which M. Agassiz has established his classification of recent Fishes is in a peculiar degree applicable to fossil Fishes, being founded on the character of the external coverings, or Scales. This character is so sure and constant, that the preservation, even of a single scale, will often announce the genus and even the species of the animal from which it was derived; just as certain feathers announce to a skilful ornithologist the genus or species of a Bird. It follows still further, that as the nature of their outward covering indicates the relations of all animals to the external world, we derive from their scales certain indications of the relations of Fishes; * the scales forming a kind of external skeleton, analogous to the crustaceous or

* The foundation of this character is laid upon the dermal covering, the skin being that organ which, more than any other part of the body, shows the relation of every animal to the element in which it moves.

The form and conditions of the feathers and down show the relation of Birds to the air in which they fly, or the water in which they swim or dive. The varied forms of fur and hair and bristles on the skins of Beasts are adapted to their respective place, and climate, and occupations upon the land. The scales of Fishes show a similar adaptation to their varied place and occupations beneath the waters.

Mr. Burchell informs me that he has observed, both in Africa and South America, that in the order of Serpents a peculiar character of the scales appears to indicate a natural subdivision; and that in that tribe, to which the Viper, and nearly all the venomous Snakes belong, an acute ridge, or carina, along each dorsal scale may be considered as a distinctive mark.

[269 CHARACTERS DERIVED FROM SCALES.] horny coverings of Insects, to the feathers of Birds, and the fur of Quadrupeds, which shows more directly than the internal bones, their adaptation to the medium in which they lived.

A further advantage arises from the fact that the enamelled condition of the scales of most Fishes, which existed during the earlier geological epochs, rendered them much less destructible than their internal skeleton; and cases frequently occur where the entire scales and figure of the Fish are perfectly preserved, whilst the bones within these scales have altogether disappeared; the enamel of the scales being less soluble than the more calcareous material of the bone.*

* The following are the new Orders into which M . Agassiz divides the Class of Fishes.

First Order, PLACOIDIANS. (Pl. 27, Figs. 1, 2, Etym. , a broad plate.) Fishes of this Order are characterized by having their skin covered irregularly with plates of enamel, often of considerable dimensions, and sometimes reduced to small points, like the shagreen on the skins of many Sharks, and the prickly, tooth-like tubercles on the skin of Rays. It comprehends all the cartilaginous fishes of Cuvier, excepting the Sturgeon.

The enamelled prickly tubercles on the skin of Sharks and Dog-Fishes are well known, from the use made of them in rasping and polishing wood, and for shagreen.

Second Order, GANOIDIANS. (Pl. 27, 3, 4, Etym. , splendour, from the bright surface of their enamel.) The families of this Order are characterized by angular scales, composed of horny or bony plates, covered with a thick plate of enamel. The bony Pike (Lepidosteus Osseus, Pl. 27^a Fig. 1);

[270 FOSSIL FISHES.] It must be obvious that another and most important branch of natural history is enlisted in aid of Geology, as soon as the study of the character of fossil Fishes has been established on any footing, which admits of such general application as the system now proposed. We introduce an additional element into geological calculations; we bring an engine of great power, hitherto unapplied, to bear on the field of our enquiry, and seem almost to add a new sense to our powers of geological perception. The general result is, that fossil Fishes approximate

and Sturgeons are of this Order. It contains more than sixty genera, of which fifty are extinct.

Third Order, CTENOIDIANS. (Pl. 27, Figs. 5, 6, Etym. , a comb.) The Ctenoidians have their scales jagged or pectinated, like the teeth of a comb, on their posterior margin. They are formed of laminæ of horn or bone, but have no enamel. The Perch affords a familiar example of scales constructed on this principle.

Fourth Order, CYCLOIDIANS. (Pl. 27, Figs. 7, 8. Etym. , a circle.) Families of this Order have their scales smooth, and simple at their margin, and often ornamented with various figures on the upper surface: these scales are composed of laminæ of horn or bone, but have no enamel. The Herring and Salmon are examples of Cycloidians.

Each of these Orders contains both cartilaginous and bony Fishes: the representatives of each prevailed in different proportions during different epochs; only the two first existed before the commencement of the Cretaceous formations; the third and fourth Orders, which contain three-fourths of the eight thousand known species of living Fishes, appear for the first time in the Cretaceous strata, when all the preceding fossil genera of the two first Orders had become extinct.

[271 CHANGES OF GENERA, AND SPECIES.] nearest to existing genera and species, in the most recent Tertiary deposits; and differ from them most widely in strata whose antiquity is the highest; and that strata of intermediate age are marked by intermediate changes of ichthyological condition.

It appears still further, that all the great changes in the character of fossil Fishes take place simultaneously with the most important alterations in the other classes of fossil animals, and in fossil vegetables; and also in the mineral condition of the strata.*

It is satisfactory to find that these conclusions are in perfect accordance with those to which geologists had arrived from other data. The details that lead to them, will be described by M. Agassiz, in a work of many volumes, and will form a continuation of the Ossemens Fossiles of Cuvier. From the parts of this work already published, and from communications by the author, I select a few examples, illustrating

* The genera of Fishes which prevail in strata of the Carboniferous order are found no more after the deposition of the Zechstein, or Magnesian limestone. Those of the Oolitic series were introduced after the Zechstein, and ceased suddenly at the commencement of the Cretaceous formations. The genera of the Cretaceous formations are the first that approximate to existing genera. Those of the lower Tertiary deposits of London, Paris, and Monte Bolca, are still more nearly allied to existing forms; and the fossil Fishes of Oeningen and Aix approximate again yet closer to living genera, although every one of their species appears to be extinct.

[272 CHANGES OF GENERA SUDDEN.] the character of some of the most remarkable families of fossil Fishes.

It appears that the character of fossil Fishes does not change insensibly from one formation to another, as in the case of many Zoophytes and Testacea; nor do the same genera; or even the same families, pervade successive series of great formations; but their changes take place abruptly, at certain definite points in the vertical succession of the strata, like the sudden changes that occur in fossil Reptiles and Mammalia.* Not a single species of fossil Fishes has yet been found that is common to any two great geological formations; or living in our present seas.

One important geological result has already attended the researches of M. Agassiz, viz. that the age and place of several formations hitherto unexplained by any other character, have been made clear by a knowledge of the fossil Fishes which they contain.

* M. Agassiz observes that fossil Fishes in the same formation present greater variations of species at distant localities, than we find in the species of shells and Zoophytes, in corresponding parts of the same formation; and that this circumstance is readily explained by the greater locomotive powers of this higher class of animals.

The nodules of clay stone on the coast of Greenland, containing fishes of a species now living in the adjacent seas, (Mallotus Villosus) are probably modern concretions.

Thus the slate of Engi, in the canton of Glaris, in Switzerland,

[273 SAUROID FISHES.]

The voracious family of Sauroid, or Lizard-like Fishes, first claims our attention, and is highly important in the physiological consideration of the history of Fishes, as it combines in the structure both of the bones, and some of the soft parts, characters which are common to the class of reptiles.  M. Agassiz has already ascertained

has long been one of the most celebrated, and least
understood localities of fossil Fishes in Europe, and the mineral character of this slate had till lately caused it to be referred to the early period of the Transition series. M. Agassiz has found that among its numerous fishes, there is not one belonging to a single genus, that occurs in any formation older than the Cretaceous series; but that many of them agree with fossil species found in Bohemia, in the lower Cretaceous formation, or Pläner kalk; hence he infers that the Glaris slate is an altered condition of an argillaceous deposit, subordinate to the great Cretaceous formations of other parts of Europe, probably of the Gault.
Another example of the value of Ichthyology, in illustration of Geology, occurs in the fact, that as the fossil Fishes of the Wealden estuary formation are referrible to genera that characterize the strata of the Oolitic series, the Wealden deposits are hereby connected with the Oolitic period that preceded their commencement, and are separated from the Cretaceous formations that followed their termination. A change in the condition of the higher orders of the inhabitants of the waters seems to have accompanied the changes that occurred in the genera and species of inferior animals at the commencemerit of the Cretaceous formations.
A third example occurs, in the fact that M. Agassiz has, by resemblances in the character of their fossil Fishes, identified the hitherto unknown periods of the freshwater deposits of Oeningen, and of Aix in Provence, with that of the Molasse of Switzerland.

[274 SAUROID FISHES.] seventeen genera of Sauroid Fishes. Their only living representatives are the genus Lepidosteus,* or bony Pike (Pl. 27a, Fig. 1.), and the genus Polypterus (Agass. Poiss. Foss. Vol. 2. Tab. C.), the former containing five species, and the latter two. Both these genera are found only in fresh waters, the Lepidosteus in the rivers of North America, and the Polypterus in the Nile, and the waters of Senegal.

The teeth of the Sauroid Fishes are striated longitudinally towards the base, and have a hollow cone within. (See Pl. 27^a, 2, 3, 4; and Pl. 27. 9, 10, 11, 12, 13, 14.) The bones of the palate also are furnished with a large apparatus of teeth.

* Lepidosteus Agassiz — Lepisosteus Lacépède.

The bones of the skull, in Sauroid Fishes, are united by closer sutures than those of common Fishes. The vertebræ articulate with the spinous processes by sutures, like the vertebræ of Saurians; the ribs also articulate with the extremities of the spinous processes. The caudal vertebræ have distinct chevron bones, and the general condition of the skeleton is stronger and more solid than in other Fishes: the air-bladder also is bifid and cellular, approaching to the character of lungs, and in the throat there is a glottis, as in Sirens and Salamanders, and many Saurians. — See Report of Proceedings of Zool. Soc. London, October, 1834.

The object of the extensive apparatus of teeth, over the whole interior of the mouth of many of the most voracious Fishes, appears not to be for mastication, but to enable them to hold fast, and swallow the slippery bodies of other Fishes that form their prey. No one who has handled a living Trout or Eel can fail to appreciate duly the importance of the apparatus in question.

[275 CHARACTER AND SIZE.] Pl. 27, Figs. 11, 12, 13, 14, represent teeth of the largest Sauroid Fishes yet discovered, equalling in size the teeth of the largest Crocodiles:

they occur in the lower region of the Coal formation near Edinburgh, and are referred by M. Agassiz to a new genus, Megalichthys. Pl. 27, Fig. 9, and Pl. 27^a, Fig. 4, are fragments of jaws, containing many smaller teeth of the same kind. The external form of all these teeth is nearly conical, and within them is a conical cavity, like that within the teeth of many Saurians; their base is fluted, like the base of the teeth of the Ichthyosaurus. Their prodigious size shows the magnitude which Fishes of this family attained at a period so early as that of the Coal formation:* their structure coincides

* We owe the discovery of these very curious teeth, and much valuable information on the Geology of the neighbourhood of Edinburgh, to the zeal and discernment of Dr. Hibbert, in the spring of 1834. The limestone in which these Fishes occur lies near the bottom of the Coal formation, and is loaded with Coprolites, derived apparently from predaceous Fishes. It is abundantly charged also with ferns, and other plants of the coal formation; and with the crustaceous remains of Cypris, a genus known only as an inhabitant of fresh water. These circumstances, and the absence of Corals and Encrinites, and of all species of marine shells, render it probable that this deposit was formed in a freshwater lake, or estuary. It has been recognized in various and distant places, at the bottom of the carboniferous strata near Edinburgh.

In the Transactions of the Royal Society of Edinburgh, Vol. XIII. Dr. Hibbert has published a most interesting description of the recent discoveries made in the limestone of Burdie House,

[276 GEOLOGICAL DISTRIBUTION] entirety with that of the teeth of the living Lepidosteus osseus. (Pl. 27^a, Figs. 1, 2, 3.)

Smaller Sauroid Fishes only have been noticed in the Magnesian limestone, forming about one-fifth of the total number yet observed in this formation. Very large bones of this voracious family occur in the lias of Whitby and Lyme Regis, and its genera abound throughout the Oolite formation.* In the Cretaceous formations they become extremely rare. They

illustrated with engravings, from which the larger teeth in our plate are copied. (Pl. 27, Fig. 11, 12, 13, 14). The smaller figures, Pl. 27, Fig. 9, and Pl. 27^a Fig. 4, are drawn from specimens belonging to Dr. Hibbert and the Royal Society of Edinburgh.

In this memoir, Dr. Hibbert has also published figures of some curious large scales, found at Burdie House, with the teeth of Megalichthys, and referred by M . Agassiz to that Fish. Similar scales have been noticed in various parts of the Edinburgh Coal field, and also in the Coal formation of Newcastle-on-Tyne. Unique specimens of the heads of two similar Fishes, and part of a body covered with scales, from the Coal field near Leeds, are preserved in the museum of that town.

Sir Philip Grey Egerton has recently discovered scales of the Megalichthys, with teeth and bones of some other Fishes, and also Coprolites, in the Coal formation of Silverdale, near Newcastle-under-Line. These occur in a stratum of shale, containing shells of three species of Unio, with balls of argillaceous iron ore and plants.

* The Aspidorhynchus, from the Jurassic limestone of Solenhofen, (Pl . 27^a Fig. 5), represents the general character of the sauroid Fishes.

The Macropoma is the only genus of Sauroid Fishes yet found in the Chalk of England.

[277 OF SAUROID FISHES.] have not yet been discovered in any of the Tertiary strata; and in the waters of the present world are reduced to the two genera, Lepidosteus and Polypterus.

Thus we see that this family of Sauroids holds a very important place in the history of fossil Fishes. In the waters of the Transition period, the Sauroids and Sharks constituted the chief voracious forms, destined to fulfil the important office of checking excessive increase of the inferior families. In the Secondary strata, this office was largely shared by Ichthyosauri and other marine Saurians, until the commencement of the Chalk. The cessation of these Reptiles and of the semi-reptile Sauroid Fishes in the Tertiary formations made room for the introduction of other predaceous families, approaching more nearly to those of the present creation.*

* Much light has been thrown on the history of Fishes in the Old red sandstone at the base of the Carboniferous series, by the discoveries of Professor Sedgwick and Mr. Murchison, in the bituminous schist of Caithness, (Geol. Trans. Lond. N. S. Vol. 3, part 1.); and those of Dr. Traile, in the same schist in Orkney. Dr. Fleming also has made important observations on Fishes in the old red sandstone of Fifeshire. Further discoveries have been made by Mr. Murchison of Fishes in the old red sandstone of Salop and Herefordshire. The general conditions of all these Fishes accord with those in the carboniferous series, but their specific details present most interesting peculiarities. Many of them will be figured by Mr. Murchison in his splendid Illustrations of the Geology of the Border Counties of England and Wales.

278 FOSSIL FISHES,]

I select the genus Amblypterus (Pl. 27^b.), as an example of Fishes whose duration was limited to the early periods of geological Formations; and which are marked by characters that cease after the deposition of the Magnesian limestone.

This genus occurs only in strata of the Carboniferous order, and presents four species at Saarbrück, in Lorraine;* it is found also in Brazil. The character of the teeth in Amblypterus, and most of the genera of this early epoch, shews the habit of these Fishes to have been to feed on decayed sea-weed, and soft animal substances at the bottom of the water: they are all small and numerous, and set close together like a brush. The form of the body, being not calculated for rapid progression, accords with this habit.

* The Fishes at Saarbrück are usually found in balls of clay ironstone, which form nodules in strata of bituminous coal shale. Lord Greenock has recently discovered many interesting examples of this, and other genera of Fishes in the coal formation at Newhaven, and Wardie, near Leith. The shore at Newhaven is strewed with nodules of ironstone, washed out by the action of the tide, from shale beds of the coal formation. Many of these ironstones have for their nucleus a fossil Amblypterus, or some other Fish; and an infinitely greater number contain Coprolites, apparently derived from a voracious species of Pygopterus, that preyed upon the smaller Fishes.

[279 IN THE CARBONIFEROUS STRATA.] The vertebral column continues into the upper lobe of the tail, which is much longer than the lower lobe, and is thus adapted to sustain the body in an inclined position, with the head and mouth nearest to the bottom.

Among existing cartilaginous Fishes, the vertebral column is prolonged into the caudal fin of Sturgeons and Sharks: the former of these perform the office of scavengers, to clear the water of impurities, and have no teeth, but feed by means of a soft leather-like mouth, capable of protrusion and contraction, on putrid vegetables and animal substances at the bottom; hence they have constant occasion to keep their bodies in the same inclined position as the extinct fossil Fishes, whose feeble brush-like teeth shew that they also fed on soft substances in similar situations.*

The Sharks employ their tail in another peculiar manner, to turn their body in order to bring the mouth, which is placed downwards beneath the head, into contact with their prey. We find an important provision in every animal to give a position of ease and activity to the head during the operation of feeding. 

* At the siege of Silistria, the Sturgeons of the Danube were observed to feed voraciously on the putrid bodies of the Turks and Russian soldiers that were cast into that river.

This remarkable elongation of the superior lobe of the tail is found in every bony Fish of strata anterior to and including the Magnesian limestone ; but in strata above this limestone the

[280 FISHES IN MAGNESIAN LIMESTONE,]
 

The Fishes of the Zechstein at Mansfeld and Eisleben have been long known, and are common in all collections; figures of many species are given by M . Agassiz. Examples of the Fishes of the Magnesian limestone of the north of England, are described and figured by Professor Sedgwick, in the Geol. Trans. of London, (2d Series, Vol. iii. p. 117, and Pl. 8, 9, 10). He states in this paper (p. 99), that the occurrence of certain Corals and Encrinites, and several species of Producta, Arca, Terebratula, Spirifer, &c. shews that the Magnesian limestone is more nearly allied in its zoological characters to the Carboniferous order, than to the calcareous formations which are superior to the New red sandstone. This conclusion accords with that which M. Agassiz has drawn from the character of its fossil Fishes.

tail is regular and symmetrical. In certain bony Fishes of the secondary period, the upper lobe of the tail is partly covered with scales, but without vertebræ. The bodies of all these Fishes also have an integument of rhomboidal bony scales, covered with enamel.

No species of Fish has been found common to the Carboniferous group, and to the Zechstein or Magnesian limestone; but certain genera occur in both, e. g. the genus Palæoniscus and Polypterus.

[281 MUSCHEL-KALK, LIAS, AND OOLITE.]

The Fishes of the Muschelkalk are either peculiar to it, or similar to those of the Lias and Oolite. The figure engraved at Pl. 27^c, is selected as an example of the character of a family of Fishes most abundant in the Jurassic or Oolite formation; it represents the genus Microdon in the family of Pycnodonts, or thick-toothed Fishes, which prevailed extensively during the middle ages of Geological History. Of this extinct family there are five genera. Their leading character consists in a peculiar armature of all parts of the mouth with a pavement of thick round and flat teeth, the remains of which, under the name of Bufonites, occur most abundantly throughout the Oolite formation The use of this peculiar apparatus was to crush small shells, and small Crustacea, and to comminute putrescent sea-weeds. The habits of the family of Pycnodonts appear to have been omnivorous, and their power of progression slow.

* Pl. 27^c. Fig. 3. represents a five-fold series of these teeth on the palate of Pycnodus trigonus from Stonesfield; and Fig. 2, a series of similar teeth placed on the vomer in the palate of the Gyrodus Umbilicus from the great Oolite of Durrheim, in Baden.

A similar apparatus occurs in a living family of the Order Cycloids, in the case of the modern omnivorous Sea Wolf,

[282 LEPIDOID FISHES.] Another family of these singular Fishes of the ancient world, which was exceedingly abundant in the Oolitic or Jurassic series, is that of the Lepidoids, a family still more remarkable than the Pycnodonts for their large rhomboidal bony scales, of great thickness, and covered with beautiful enamel. The Dapedium of the lias (Pl. 1. Fig. 64.) affords an example of these scales, well known to geologists. They are usually furnished on their upper margin with a large process or hook, placed like the hook or peg near the upper margin of a tile; this hook fits into a depression on the lower margin of the scales placed next above it. (See Pl. 27, Figs. 3, 4, and Pl. 15, Fig. 17.) All Ganoidian Fishes, of every formation, prior to the Chalk, were enclosed in a similar cuirass, composed of bony scales, covered with enamel, and extending from the head to the rays of the tail.* One or two species only, having this peculiar armature of enamelled bony scales,

Anarrhicas Lupus, and other recent Fishes of different families. M. Agassiz observes, that it is a common fact, in the class of Fishes, to find nearly all the modifications which the teeth of these animals present, recurring in several families, which in other respects are very different.

The Pycnodonts, as well as the fossil Sauroids, have enamelled scales, but it is in the Lepidoids that scales of this kind are most highly developed. M. Agassiz has ascertained nearly 200 fossil species that had this kind of armour. The use of such an universal covering of thick bony and enamelled scales, surrounding like a cuirass the entire bodies of so many species of Fishes, in all formations anterior to the Cretaceous deposits, may have been to defend their bodies against waters

[283 FISHES IN CHALK FORMATION.] have yet been discovered in the Cretaceous series; and three or four species in the Tertiary formations. Among living Fishes, scales of this kind occur only in the two genera, Lepidosteus and Polypterus.

Not a single genus of all that are found in the Oolitic series exists at the present time. The most abundant Fishes of the Wealden formation belong to genera that prevailed through the Oolitic period.*

The next and most remarkable of all changes in the character of Fishes, takes place at the commencement of the Cretaceous formations. Genera of the first and second orders (Phacoidean and Ganoidian), which had prevailed exclusively in all formations till the termination of the Oolitic series, ceased suddenly, and were replaced by genera of new orders (Ctenoidean and Cycloidean), then for the first time introduced. Nearly two-thirds of the latter also are now extinct; but these approach nearer to Fishes of the tertiary series, than to those which had preceded the formation of the Chalk.

that were warmer, or subject to more sudden changes of temperature, than could be endured by Fishes whose skin was protected only by such thin, and often disconnected coverings, as the membranotis and horny scales of most modern Fishes.

* The most. remarkable of these are the genus Lepidotus, Pholidophorus, Pycnodus, and Hybodus.

[284 FOSSIL FISHES,] Comparing the Fishes of the Chalk with those of the elder Tertiary formation of Monte Bolca, we find not one species, and but few genera, that are common to both.*

As soon as we enter on the Tertiary strata, another change takes place in the character of fossil Fishes, not less striking than that in fossil Shells.

The fishes of Monte Bolca are of the Eocene period, and are well known by the figures engraved in the Ittiolitologia Veronese, of Volta; and in Knorr. About one-half of these fishes

* It has been already stated, that the remarkable deposit of fossil Fishes at Engi, in the Canton of Glaris, are referred by M. Agassiz to the lower portion of the Cretaceous system.

Many genera of these are identical with, and others closely approximate to, the fishes of the Inferior chalk (Pläner kalk) of Bohemia, and of the Chalk of Westphalia (see Leonhard and Bronn. Neues Jahrbuch, 1834). Although the mineral character of the slate of Glaris presents, as we have before stated, an appearance of high antiquity, its age is probably the same as that of the Gault, or Speeton clay of England. This alteration of character is consistent with the changes that have given an air of higher antiquity than belongs to them, to most of the Secondary and Tertiary formations in the Alps.

The Fishes of the Upper chalk are best known by the numerous and splendid examples discovered at Lewes by Mr. Mantell, and figured in his works. These Fishes are in an unexampled state of perfection; in the abdominal cavities of one species (Macropoma) the stomach, and coprolites are preserved entire, in their natural place.

[285 IN THE TERTIARY FORMATIONS.] belong to extinct genera, and not one is identical with any existing species; they are all marine, and the greater number approach most nearly to forms now living within the tropics.*

To this first period of the Tertiary formations belong also the Fishes of the London clay; many of the species found in Sheppy, though not identical with those of Monte Bolca, are closely allied to them. The Fishes of Libanus also are of this era. The Fishes in the gypsum of Mont Martre are referred to the same period by M. Agassiz, who differs from Cuvier, in at tributing them all to extinct genera.

The Fishes of Oeningen have, by all writers, been referred to a very recent local lacustrine deposit. M. Agassiz assigns them to the second period of the Tertiary formations, coeval with the Molasse of Switzerland and the sandstone of Fontainbleau. Of seventeen extinct species, one only is of an extra-European genus, and all belong to existing genera.

The gypsum of Aix contains some species referrible to one of the extinct genera of Mont Martre, but the greatest part are of existing genera. M. Agassiz considers the age of this formation

* M. Agassiz has re-arranged these fishes under 127 Species, all extinct, and 77 Genera. Of these Genera 38 are extinct, and 39 still living; the latter present 81 fossil species at Monte Bolca, and the former 46 species. These 39 living Genera appear for the first time in this formation.

[286 FOSSIL SHARKS.] as nearly coinciding with that of the Oeningen deposits.

The Fishes of the Crag of Norfolk, and the superior Sub-apennine formation, as far as they are yet known, appear for the most part related to genera now common in tropical seas, but are all of extinct species.

As the family of Sharks is one of the most universally diffused and most voracious among modern Fishes, so there is no period in geological history in which many of its forms did not prevail.* Geologists are familiar with the occurrence of various kinds of large, and beautifully enamelled teeth, some of them resembling the external form of a contracted leech, (Pl. 27^e, and 27^f): these are commonly described by the name of Palate bones, or Palates. As these teeth are usually insulated, there is little evidence to indicate from what animals they have been derived.

In the same strata with them are found large bony Spines, armed on one side with prickles resembling hooked teeth, (see Pl 27^d. C. 3. a.) These were long considered to be jaws, and true teeth; more recently they have been ascertained

* M. Agassiz has ascertained the existence of more than one hundred and fifty extinct species of fossil Fishes allied to this family.

[287 THREE SUB-FAMILIES.] to be dorsal spines of Fishes, and from their supposed defensive office, like those of the genus Balistes and Silurus, have been named Ichthyodorulites .

M. Agassiz has at length referred all these bodies to extinct genera in the great family of Sharks, a family which he separates into three sub-families, each containing forms peculiar to certain geological epochs, and which change simultaneously with the other great changes in fossil remains.

The first and oldest sub-family, Cestracionts, beginning with the Transition strata, appears in every subsequent formation, till the commencement of the Tertiary, and has only one living representative, viz, the Cestracion Philippi, or Port Jackson Shark. (Pl. l. Fig. 18.) The second family, Hybodonts, beginning with the Muschel-kalk, and perhaps with the Coal formation, prevails throughout the Oolite series, and ceases at the commencement of the Chalk. The third family of " Squaloids," or true Sharks, commences with the Cretaceous formation, and extends through the Tertiary strata into the actual creation.*

* The character of the Cestracionts is marked by the presence of large polygonal obtuse enamelled teeth, covering the interior of the mouth with a kind of tesselated pavement. (Pl. 27^d. A. I, 3, 4, and Pl. 27^d, B. 1, 2, 3, 4. 5.) In some species not less than sixty of these teeth occupied each jaw. They are rarely found connected together in a fossil state, in consequence of the

[288 BONY SPINES OF SHARKS.]

The bony spines of the dorsal fins of the Port Jackson Shark (Pl. l. Fig. 18.) throw important light on the history of fossil Spines; and enable

perishable nature of the cartilaginous bones to which they were attached; hence the spines and teeth usually afford the only evidence of the former existence of these extinct fossil species. They are dispersed abundantly throughout all strata, from the Carboniferous series to the most recent Chalk.

In Plate 27^e, Figs . 1, 2, represent a series of teeth of the genus Acrodus, in the family of Cestracionts, from the has of Somersetshire; and Pl. 27^f, a series of teeth of the genus Ptychodus, in the same family, a genus which occurs abundantly and exclusively in the Chalk formation.

In the section Pl. 1, Fig. 19 represents a tooth of Psammodus, and Fig. 19', a tooth of Orodus, from the Carboniferous limestone; and Fig. 18', a recent tooth of the Cestracion Philippi. The Cestracion Philippi,- (Pl. 1, Fig. 18, and Pl. 27^d, A.) is the only living species in the family of Sharks that has flat tesselated teeth, and enables us to refer numerous fossil teeth of similar construction to the same family. As the small anterior cutting teeth (Ph. 27^d, A. Figs. 1. 2. 5.) in this species, present a character of true Sharks, which has not been found in any of the fossil Cestracionts, we have in this dentition of a living species, the only known link that connects the nearly extinct family of Cestracionts with the true Sharks or Squaloids.

The second division of the family of Sharks, Hybodonts, commencing probably with the Coal formation, prevailed during the deposition of all the Secondary strata beneath the Chalk; the teeth of this division possess intermediate characters between the blunt polygonal crushing teeth of the sub-family Cestracion, and the smooth and sharp-edged cutting teeth of the Squaloids, or true Sharks, which commenced with the Cretaceous formations. They

* See Pl. 27^d. C. 3.

[289 ICHTHYODORULITES.] us to refer those very common, but little understood fossils, which have been called Ichthyodorulites, to extinct genera and species of the subfamily of Cestracionts. (See page 286). Several living species of the great family of Sharks have

are distinguished from those of true Sharks by being plicated, both on the external and internal surface of the enamel. (See Plate 27^d. B. Figs. 8, 9, 10). Plate 27^d C. l.^re represents a rare example of a series of teeth of Hybodus reticulatus, still adhering to the cartilaginous jaw bones, from the lias of Lyme Regis. Striated teeth of this family abound in the Stonesfield slate arid in the Wealden formation.

Another genus in the sub-family of Hybodonts, is the Onchus, found in the Lias at Lyme Regis; the teeth of this genus are represented, Pl. 27^d. B. 6, 7.

In the third, or Squaloid division of fossils of this family, we have the character of true Sharks; these appear for the first time in the Cretaceous formations, and extend through all the Tertiary deposits to the present era. (Pl. 27^d. B. 11, 12, 13.) In this division the surface of the teeth is always smooth on the outer side, and sometimes plicated on the inner side, as it is also in certain living species; the teeth are often flat and lancet~shaped, with a sharp cutting border, which, in many species, is serrated with minute teeth. Species of this Squaloid family alone, abound in all strata of the Tertiary formation.

The greater strength, and flattened condition of the teeth of the families of Sharks (Cestracionts and Hybodonts), that prevailed in the Transition and Secondary formations beneath the Chalk, had relation, most probably, to their office of crushing the hard coverings of the Crustacca, and of the bony enamelled scales of the Fishes, which formed their food. As soon as Fishes of the Cretaceous and Tertiary formations assumed the softer scales of modern Fishes, the teeth of the Squaloid sub-family assumed the sharp and cutting edges that characterise the teeth of living Sharks. Not one species of the blunt-toothed Cestraciont family has yet been discovered in any Tertiary formation.

[290 BONY SPINES OF SHARKS.] smooth horny spines connected with the dorsal fin. In the Cestracion Philippi alone, (Pl. 1, Fig. 18), we find a bony spine armed on its concave side with tooth-like hooks, or prickles, similar to those that occur in fossil lchthyodorulites: these hooks act as points of suspension and attachment, whereby the dorsal fin is connected with this bony spine, and its move ments regulated by the elevation or depression of the spine, during the peculiar rotatory action of the body of Sharks. This action of the spine in raising and depressing the fin resembles that of a moveable mast, raising and lowering backwards the sail of a barge.

The common Dog-Fish, or Spine Shark, (Spinax Acanthias, Cuv.), and the Centrina Vulgaris, have a horny elevator spine on each of their dorsal fins, but without teeth or hooks; similar small toothless horny spines have been found by Mr. Mantell in the chalk of Lewes. These dorsal spines had probably a further use as offensive and defensive weapons against voracious fishes, or against larger and stronger individuals of their own species.*

The variety we find of fossil spines, from the Greywacke series to the Chalk inclusive, indicates

* Colonel Smith saw a captain of a vessel in Jamaica who received many severe cuts in the body from the spines of a Shark in Montego Bay. (See Griffith's Cuvier.)

The Spines of Balistes and Silurus have not their base, like that of the spines of Sharks, simply imbedded in the flesh, and

[291 FOSSIL RAYS.] the number of extinct genera and species of the family of Sharks, that occupied the waters throughout these early periods of time. Not less varied are the forms of palate bones and teeth, in the same formations that contain these spines; but as the cartilaginous skeletons to which they belonged have usually perished, and the teeth and spines are generally dispersed, it is chiefly by the aid of anatomical analogies, or from occasional juxtaposition in the same stratum, that their respective species can be ascertained.

The Rays form the fourth family in the order Placoidians.
Genera of this family abound among living fishes; but they have not been found fossil in any stratum older than the Lias; they occur also in the Jurassic limestone.

Throughout the tertiary formation they are very abundant; of one genus, Myliobates, there are seven known species; from these have been derived the palates that are so frequent in the
London clay and crag. (See Pl. 27^d, B. Fig. 14.) The genus Trygon, and Torpedo, occur also in the Tertiary formations.

attached to strong muscles; but articulate with a bone beneath them. The Spine of Balistes also is kept erect by a second spine behind its base, acting like a bolt or wedge, which is simultaneously inserted, or withdrawn, by the same muscular motion that raises or depresses the spine.

[292 GENERAL CONCLUSION.]

In the facts before us, we have an uninterrupted series of evidence, derived from the family of Fishes, by which both bony and cartilaginous forms of this family, are shewn to have prevailed during every period, from the first commencement of submarine life, unto the present hour. The similarity of the teeth, and scales, and bones, of the earliest Sauroid Fishes of the coal formation (Megalichthys), to those of the living Lepidosteus, and the correspondence of the teeth and bony spines of the only living Cestraciont in the family of Sharks, with the numerous extinct forms of that sub-family, which abound throughout the Carboniferous and Secondary formations, connect extreme points of this grand vertebrated division of the animal kingdom, by one unbroken chain, more uniform and continuous than has hitherto been discovered in the entire range of geological researches .

It results from the review here taken of the history of fossil Fishes, that this important class of vertebrated animals presented its actual gradations of structure amongst the earliest inhabitants of our planet; and has ever performed the same important functions in the general economy of nature, as those discharged by their living representatives in our modern seas, and

[293 COMMON OBJECT OF CREATION.] lakes, and rivers. The great purpose of their existence seems at all times to have been, to fill the waters with the largest possible amount of animal enjoyment.

The sterility and solitude which have some times been attributed to the depths of the ocean, exist only in the fictions of poetic fancy. The great mass of the water that covers nearly three-fourths of the globe is crowded with life, perhaps more abundantly than the air, and the surface of the earth; and the bottom of the sea, within a certain depth accessible to light, swarms with countless hosts of worms, and creeping things, which represent the kindred families of low degree which crawl upon the land.

The common object of creation seems ever to have been, the infinite multiplication of life. As the basis of animal nutrition is laid in the vegetable kingdom, the bed of the ocean is not less beautifully clothed with submarine vegetation, than the surface of the dry land with verdant herbs and stately forests. In both cases, the undue increase of herbivorous tribes is controlled by the restraining influence of those which are carnivorous; and the common result is, and ever has been, the greatest possible amount of animal enjoyment to the greatest number of individuals.

From no kingdom of nature does the doctrine of gradual Development and Transmutation of

[294 RETROGRADE DEVELOPMENT.] species derive less support, than from the progression we have been tracing in the class of Fishes. The Sauroid Fishes occupy a higher place in the scale of organization, than the ordinary forms of bony Fishes; yet we find examples of Sauroids of the greatest magnitude, and in abundant numbers in the Carboniferous and Secondary formations, whilst they almost disappear and are replaced by less perfect forms in the Tertiary strata, and present only two genera among existing Fishes.

In this, as in many other cases, a kind of  retrograde development, from complex to simple forms, may be said to have taken place. As some of the more early Fishes united in a single species, points of organization which, at a later period, are found distinct in separate families, these changes would seem to indicate in the class of Fishes a process of Division, and of Subtraction from more perfect, rather than of Addition to less perfect forms.

Among living Fishes, many parts in the or ganization of the Cartilaginous tribes, (e. g. the brain, the pancreas, and organs subservient to generation,) are of a higher order than the corresponding parts in the Bony tribes; yet we find the cartilaginous family of Squaloids co-existing with bony fishes in the Transition strata, and extending with them through all geological formations, unto the present time.

[295] In no kingdom of nature, therefore, does it seem less possible to explain the successive changes of organization, disclosed by geology, without the direct interposition of repeated acts of Creation.