Geology and Mineralogy considered with reference to Natural Theology/Chapter 14

by William Buckland

CHAPTER XIV.

Proofs of design in the Structure of Fossil Vertebrated Animals.

SECTION I.

FOSSIL MAMMALIA.—DINOTHERIUM.

Enough has, I trust, been stated in the preceding chapter, to show the paramount importance of appealing to organic remains, in illustration of that branch of physico-theology with which we are at present occupied.

The structure of the greater number, even of the earliest fossil Mammalia, differs in so few essential points from that of the living representatives of their respective Orders, that I forbear to enter on details which would indeed abound with evidences of creative design, but would offer little that is not equally discoverable in the anatomy of existing species. I shall, therefore, limit my observations to two extinct genera, which are perhaps the most remarkable of all fossil Mammalia, for size and unexampled peculiarities of anatomical construction; the first of these, the Dinotherium, having been the largest of terrestrial Mammalia;^[1] and the second, the Megatherium, presenting greater deviations from ordinary animal forms, than occur in any other species, either of recent or of fossil quadrupeds.

It has been already stated; in our account of the Mammalia of the Miocene period of the tertiary series, that the most abundant remains of the Dinotherium are found at Epplesheim, in the province of Hesse Darmstadt, and are described, in a work now in process of publication, by Professor Kaup. Fragments of the same genus are mentioned by Cuvier, as occurring in several parts of France, and in Bavaria and Austria.

The form of the molar teeth of the Dinotherium (Pl. 2, C. Fig. 3), so nearly resembles that of the Tapirs, that Cuvier at first referred them to a gigantic species of this genus. Professor Kaup has since placed this animal in the new genus Dinotherium, holding an intermediate place between the Tapir and the Mastodon, and supplying another important extinct link in the great family of Pachydermata. The largest species of this genus, D. Giganteum, is calculated, both by Cuvier and Kaup, to have attained the extraordinary length of eighteen feet. The most remarkable bone of the body yet found is the shoulder-blade, the form of which more nearly resembles that of a Mole than of any other animal, and seems to indicate a peculiar adaptation of the fore, leg to the purposes of digging, an indication which is corroborated by the remarkable structure of the lower jaw.

The lower jaws of two species of Dinotherium, figured in Plate 2. C. Figs. 1. 2. exhibit peculiarities in the disposition of the tusks, such as are found in no other living or fossil animal.

The form of the molar teeth, Pl. 2. C. Fig. 3, approaches, as we have stated, most nearly to that of the molar teeth in Tapirs; but a remarkable deviation from the character of Tapirs, as well as of every other quadruped, consists in the presence of two enormous tusks, placed at the anterior extremity of the lower jaw, and curved downwards, like the tusks in the upper jaw of the Walrus. (Pl. 2. C. 1. 2.)

I shall confine my present remarks to this peculiarity in the position of the tusks, and endeavour to show how far these organs illustrate the habits of the extinct animals in which they are found. It is mechanically impossible that a lower jaw, nearly four feet long, loaded with such heavy tusks at its extremity, could have been otherwise than cumbrous and inconvenient to a quadruped living on dry land. No such disadvantage would have attended this structure in a large animal destined to live in water; and the aquatic habits of the family of Tapirs, to which the Dinotherium was most nearly allied, render it probable that, like them, it was an inhabitant of fresh water lakes and rivers. To an animal of such habits, the weight of the tusks sustained in water would have been no source of inconvenience; and, if we suppose them to have been employed, as instruments for raking and grubbing up by the roots large aquatic vegetables from the bottom, they would, under such service, combine the mechanical powers of the pick-axe with those of the horse-harrow of modern husbandry. The weight of the head, placed above these downward tusks, would add to their efficiency for the service here supposed, as the power of the harrow is increased by being loaded. with weights.

The tusks of the Dinotherium may also have been applied with mechanical advantage to hook the head of the animal to the bank. with the nostrils sustained above the water, so as to breathe securely during sleep, whilst the body remained floating, at perfect ease, beneath the surface: the animal might thus repose, moored to the margin of a lake or river, without the slightest muscular exertion, the weight of the head and body tending to fix and keep the tusks fast anchored in the substance of the bank; as the weight of the body of a sleeping bird keeps the claws clasped firmly around its perch. These tusks might have been further used, like those in the upper jaw of the Walrus, to assist in dragging the body out of the water; and also as formidable instruments of defence.

The structure of the scapula, already noticed, seems to show that the fore leg was adapted to co-operate with the tusks and teeth, in digging and separating large vegetables from the bottom. The great length attributed to the body, would have been no way inconvenient to an animal living in the water, but attended with much mechanical disadvantage to so weighty a quadruped upon land. In all these characters of a gigantic, herbivorous, aquatic quadruped, we recognise adaptations to the lacustrine condition of the earth, during that portion of the tertiary periods, to which the existence of these seemingly anomalous creatures appears to have been limited.

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SECTION II.

MEGATHERIUM.

As it will be quite impossible, in the present Treatise, to give particular descriptions of the structure, even of a few of the fossil Mammalia, which have been, as it were, restored again to life by the genius and industry of Cuvier; I shall endeavour to illustrate, by the details of a single species, the method of analytical investigation, that has been applied by that great philosopher to the anatomy both of fossil and recent animals.

The result of his researches, as recorded in the Ossemens Fossiles, has been to show that all fossil quadrupeds, however differing in generic or specific details, are uniformly constructed on the same general plan, and systematic basis of organization as living species; and that throughout the various adaptations of a common type to peculiar functions, under different conditions of the earth, there prevails such universal conformity of design, that we cannot rise from the perusal of these inestimable volumes, without a strong conviction of the agency of one vast and mighty Intelligence, ever directing the entire fabric, both of past and present systems of creation.

Nothing can exceed the accuracy of the severe and logical demonstrations, that fill these volumes with proofs of wise design, in the constant relation of the parts of animals to one another, and to the general functions of the whole body. Nothing can surpass the perfection of his reasoning, in pointing out the beautiful contrivances, which are provided in almost endless variety, to fit every living creature to its own peculiar state and mode of life. His illustration of the curious conditions, and concurrent compensations that are found in the living Elephants, apply equally to the extinct fossil species of the same genus; and similar exemplifications may be extended from the living to the extinct species of other genera, e. g. Rhinoceros, Hippopotamus, Horse, Ox, Deer, Tiger, Hyæna, Wolf; &c. that are usually associated with the Elephant in the fossil state.

The animal I shall select for my present purpose is that most extraordinary fossil creature, the Megatherium, (see Pl. 5), an animal, in some parts of its organization, nearly allied to the Sloth, and, like the Sloth, presenting an apparent monstrosity of external form, accompanied by many strange peculiarities of internal structure, which have hitherto been but little understood.

The Sloths have afforded a remarkable exception to the conclusions which naturalists have usually drawn, from their study of the organic structure and mechanism of other animals. The adaptation of each part of the body of the Elephant, to produce extraordinary strength, and of every member of the Deer and Antelope to give agility and speed are too obvious to have escaped the attention of any scientific observer; but, it has been the constant practice of naturalists, to follow Buffon in misrepresenting the Sloths, as the most imperfectly constructed among all the members of the animal kingdom, as creatures incapable of enjoyment, and formed only for misery.

The Sloth does, indeed, afford the greatest deviations from the ordinary structure of the living quadrupeds; and these have been erroneously considered as imperfections in its organization, without any compensating advantage. I have elsewhere^[2] attempted to show that these anomalous conditions are so far from being defects, or sources of inconvenience in the Sloth, that they afford striking illustrations of the varied contrivances, whereby the structure of every creature is harmoniously adapted to the state in which it was destined to live. The peculiarities of the Sloth, that render its movements so awkward on the earth, are fitted with much advantage to its destined office of living entirely upon trees, and feeding on their leaves: so also, if we consider the Megatherium with a view to its province of digging and feeding upon roots, we shall, in this habit, discover the explanation of its unusual structure, and apparently incongruous proportions; and find, in every organ, a relation of obvious convenience, and of adaptation to the office it had to discharge.^[3]

It will be my present object to enter into such a minute investigation of some of the more remarkable parts of this animal, viewing them with a constant reference to a peculiar mode of life, as may lead to the recognition of a system of well connected contrivances, in the mechanism of a creature apparently the most monstrous, and seeming to present the most ill-assorted proportions, that occur throughout the entire range of the animal kingdom.

We have here before us a gigantic quadruped, (see Pl. 5, Fig. 1,) which at first sight appears not only ill-proportioned as a whole, but whose members also seem incongruous, and clumsy, if considered with a view to the functions and corresponding limbs of ordinary quadrupeds: let us only examine them with the aid of that clue, which is our best and essential guide in every investigation of the mechanism of the animal frame; let us first infer from the total composition and capabilities of the machinery, what was the general nature of the work it was destined to perform; and from the character of the most important parts, namely, the feet and teeth, make ourselves acquainted with the food these organs were adapted to procure and masticate; and we shall find every other member of the body acting in harmonious subordination to this chief purpose in the animal economy.

In the case of ordinary animals, the passage from one form to another is so gradual, and the functions of one species receive such ample and obvious illustrations from those of the species adjacent to it, that we are rarely at a loss, to see the final cause of almost every arrangement that is presented to the anatomist. This is more especially the case with respect to the skeleton, which forms the foundation of all the other mechanisms within the body, and is of the highest importance in the history of fossil animals, of which we rarely find any other remains besides the bones, and teeth, and the scaly or osseous integuments. I select the Megatherium, because it affords an example of most extraordinary deviations, and of egregious apparent monstrosity; viz. the case of a gigantic animal exceeding the largest Rhinoceros in bulk, and to which the nearest approximations that occur in the living world, are found in the not less anomalous genera of Sloth, Armadillo, and Chlamyphorus; the former adapted to the peculiar habit of residing upon trees; the two latter constructed with unusual adaptations to the habit of burrowing in search of their food and shelter in sand; and all limited in their geographical distribution, nearly to the same regions of America that were once the residence of the Megatherium.

I shall not here enter on the unsettled questions as to the precise age of the deposites in which the Megatherium is found, or the causes by which it has been extirpated; my object is to show that the apparent incongruities of all its parts, are in reality systems of wise and well contrived adaptation to a peculiar mode of life. I proceed therefore to consider, in the order in which they are described by Cuvier, the most important organs of the Megatherium, beginning with the head, and from thence advancing to the trunk and extremities.

Head.

The bones of the head (Pl. 5, Fig. 1. a.) most nearly resemble those of a Sloth. The long and broad bone, (b,) descending the cheek from the zygomatic arch, connects it more nearly with the Ai than with any other animal: this extraordinary bone must have been auxiliary to the power of muscles, acting with more than usual advantage, in giving motion to the lower jaw (d.)

The anterior part of the muzzle (c) is so strong and substantial, and so perforated with holes for the passage of nerves and vessels, that we may be sure it supported some organ of considerable size: a long trunk was needless to an animal possessing so long a neck; the organ was probably a snout, something like that of the Tapir, sufficiently elongated to gather up roots from the ground. The septum of the nostrils also being strong and bony, gives further indication of the presence of a powerful organ appended to the nose; such an apparatus would have afforded compensation for the absence of incisor teeth and tusks. Having no incisors, the Megatherium could not have lived on grass. The structure of the molar teeth (Pl. 5, Fig. 6—11, and Pl. 6, No. 1,) shows that it was not carnivorous.

The composition of a single molar tooth resembles that of one, of the many denticules, that are united, in the compound molar of the Elephant; and affords an admirable exemplification of the method employed by Nature, whereby three substances, of unequal density, viz. ivory, enamel, and crusta petrosa, or cœmentum, are united in the construction of the teeth of graminivorous animals. The teeth are about seven inches long, and nearly of a prismatic form (Pl. 5, Fig. 7. 8.) The grinding surfaces (Pl. 5. Fig. 9. a. b. c. and Pl. 6, Z. a. b. c.) exhibit a peculiar and beautiful contrivance for maintaining two cutting wedge-shaped salient edges, in good working condition during the whole existence of the tooth; being, as I before stated, a modification of the contrivance employed in the molars of the Elephant, and other herbivore. The same principle is applied by tool-makers for the purpose of maintaining a sharp edge in axes, scythes, bill-hooks, &c. An axe, or bill-hook, is not made entirely of steel, but of one thin plate of steel, inserted between two plates of softer iron, and so enclosed that the steel projects beyond the iron, along the entire line of the cutting edge of the instrument. A double advantage results from this contrivance; first, the instrument is less liable to fracture than if it were entirely made of the more brittle material of steel; and secondly, the cutting edge is more easily kept sharp by grinding down a portion of exterior soft iron, than if the entire mass were of hard steel. By a similar contrivance, two cutting edges are produced on the crown of the molar teeth of the Megatherium. (See Pl. 6, W. X. Y. Z. and Pl. 5, Figs. 6—10.^[4])

Pl. 6, W. X. represents the manner in which each lower tooth was opposed to the tooth above it, so that the hard enamel of the one should come in contact only with the softer materials of the other; viz. the edges of the plates of enamel, (b) rubbing upon the ivory, (c;) and the enamel, (b',) upon the crusta petrosa, (a,) of the two teeth opposite to it. Hence the act of mastication formed and perpetually maintained a series of wedges, locking into each other like the alternate ridges on the rollers of a crushing-mill; and the mouth of the Megatherium became an engine of prodigious power, in which thirty-two such wedges formed the grinding surfaces of sixteen molar teeth; each from seven to nine inches long, and having the greater part of this length fixed firmly in a socket of great depth.

As the surfaces of these teeth must have worn away with much rapidity, a provision, unusual in molar teeth, and similar to that in the incisor teeth of the Beaver and other Rodentia,^[5] supplied the loss that was continually going on at the crown, by the constant addition of new matter at the root, which for this purpose remained hollow, and filled with pulp during the whole life of the animals.^[6]

It is scarcely possible to find any apparatus in the mechanism of dentition, which constitutes a more powerful engine for masticating roots, than was formed by these teeth of the Megatherium; accompanied also by a property, which is the perfection of all machinery, namely, that of maintaining itself perpetually in perfect order, by the act of performing its work.

Lower Jaw.

The lower jaw (Pl. 5, 1. d.) is very large and weighty in proportion to the rest of the head; the object of this size being to afford deep sockets for the continual growth and firm fixture of the long and vertical molar teeth; the extraordinary and strong process (b) descending from the zygomatic arch in the Megatherium, as well as in the Sloths, seems intended to support the unusual weight of the lower jaw consequent upon the peculiar form of the molar teeth.

Bones of the Trunk.

The vertebræ of the neck, though strong, are small in comparison with those towards the opposite extremity of the body; being duly proportioned to the size of a head, comparatively light, and without tusks. The dorsal portion of the vertebral column is of moderate size, but there is an enlargement of the vertebræ of the loins, corresponding with the extraordinary bulk of the pelvis and hind legs; the summits of the spinous processes, (e,) are flattened like those in the Armadillo, as if by the pressure of a cuirass.

The sacral bone, (Pl. 5, Fig. 2, a,) is united to the pelvis, (p,) in a manner peculiar to itself; and calculated to produce extraordinary strength; its processes indicate the existence of very powerful muscles for the movement of the tail. The tail was long, and composed of vertebræ of enormous magnitude, (Pl. 6, Fig. 2,) the body of the largest being seven inches in diameter, and the horizontal distance between the extremities of the two transverse processes, being twenty inches. If to this we add the thickness of the muscles and tendons, and of the shelly integument, the diameter of the tail, at its largest end, must have been at least two feet; and its circumference, supposing it to be nearly circular like the tail of the Armadillo, about six feet. These vast dimensions are not larger in proportion to the adjacent parts of the body, than those of the tail of the Armadillo, and as this animal applies its tail, to aid in supporting the weight of its body and armour, it is probable that the Megatherium made a similar use of the same organs.^[7] To the caudal vertebræ were attached also large inferior spines, or additional Chevron bones, which must have added to the strength of the tail, in assisting to support the body. The tail also probably served for a formidable instrument of defence, as in the Pangolins and Crocodiles. In 1822, Sellow saw portions of armour that had covered a tail, found near Monte Video.

The ribs are more substantial, and much thicker, and shorter, than those of the Elephant or Rhinoceros; and the upper convex surfaces of some of them exhibit a rugous and flattened condition of that part, on which the weight of a bony cuirass would most immediately have rested.

Anterior Extremity.

The scapula or shoulder blade, (Pl. 5, Fig. 1, f,) resembles that of no other family except the Sloths, and exhibits in the Acromion (g,) contrivances for strength, peculiar to itself and them, in its mode of articulation with the collar bone (h;) it exhibits also unusual provisions for the support of the most powerful muscles for the movement of the arm.

The clavicle or collar bone (h) is strong, and curved nearly as in the human subject; the presence of this bone in the Megatherium, whilst it is wanting in the Elephant, Rhinoceros, and all the large ruminating animals, shows that the fore leg discharged some other office, than that of an organ of locomotion. This clavicle would give a steady and fixed position to the socket, or glenoid cavity of the scapula, admitting of rotatory motion in the fore leg, analogous to that of the human arm. There is in these circumstances a triple accommodation to the form and habits of the Megatherium; 10. a free rotatory power of the arm was auxiliary to its office, as an instrument to be employed continually in digging food out of the ground; 2°. this act of perpetual digging in search of stationary objects like roots, required but little locomotive power; 3°. the comparatively small support afforded to the weight of the body by the fore leg, was compensated by the extraordinary and colossal strength of the haunches and hind legs. In the Elephant, the great weight of the head and tusks require shortness of neck, and unusual enlargement and strength in the fore legs; hence, the anterior parts of this animal are much stronger and larger than its hinder parts. In the case of the Megatherium, the relative proportions are reversed; the head is comparatively small, the neck is long, and the anterior part of the body but slightly loaded in comparison with its abdominal and posterior regions. In the shoulder blade and collar bone there is great provision to give strength and motion to the fore legs; but this motion is not progressive, nor is the strength calculated merely to support the weight of the body. The humerus, (k) articulates with the scapula by a round head, admitting of free motion in various directions, and is small at its upper and middle part, but at its lower end attains extraordinary breadth, in consequence of an enormous expansion of the crests, which rise from the condyles, to give origin to muscles for the movement of the fore foot and toes.^[8] The ulna (l) is extremely broad and powerful at its upper extremity, affording large space for the origin of muscles, concerned in the movements of the foot. The radius (m) revolves freely on the ulna, as in the Sloths and Ant-eaters, both of which make much use of the fore leg, though for different purposes; it has a cavity at its upper end, which turns upon a spherical portion of the lower part of the humerus, and a large apophysis (n,) projecting from its longitudinal crest, indicates great power in the muscles that gave rotatory motion.

The entire fore-foot must have been about a yard in length, and more than twelve inches wide; forming a most efficient instrument for moving the earth, from that depth within which succulent roots are usually most abundant. This great length of the fore-foot, when resting upon the ground, though unfavourable to progressive motion, must have enabled one fore-leg, when acting in conjunction with the two hind legs and tail, to support the entire weight of the body; leaving the other fore-leg at liberty to be employed exclusively in the operation of digging food.^[9]

The toes of the fore-foot are terminated by large and powerful claws of great length; the bones, supporting these claws, are composed partly of an axis, or pointed core, (o,) which filled the internal cavity of the horny claw; and partly of a bony sheath, that formed a strong case to receive and support its base. These claws were set obliquely to the ground, like the digging claws of the Mole, a position which made them instruments of greater power for the purpose of excavation.

Posterior Extremities.

The pelvis of the Megatherium (Pl. 5, Fig. 2. p.) is of vast solidity and expanse; and the enormous bones of the ileum (r) are set nearly at right angles to the spine of the back, and at their outer margin, or crest, are more than live feet asunder, very much exceeding the diameter across the haunches of the largest elephant: the crest of the ileum, (s,) is much flattened, as if by the pressure of the armour. This enormous size of the pelvis would be disproportionate and inconvenient to an animal of ordinary stature and functions; but was probably attended with much advantage to the Megatherium, in relation to its habit of standing great part of its time on three legs, whilst the fourth was occupied in digging.

The pelvis being thus, unusually wide and heavy, presents a further deviation from other animals, as to the place and direction of the acetabulum, or socket which articulates with the head of the thigh-bone (u.) This cavity, in other animals, is usually set more or less obliquely outwards, and by this Obliquity facilitates the movement of the hind-leg; but in the Megatherium it is set perpendicularly downwards, over the head of the femur, and is also nearer than usual to the spine; deriving from this position increase of strength for supporting vertical pressure, but attended with a diminished capability of rapid motion.^[10]

From the enormous width of the pelvis, it follows also that the abdominal cavity was extremely large, and the viscera voluminous, and adapted to the digestion of vegetable food.

The form and proportions of the thigh bone, (v) are not less extraordinary than those of the pelvis, being nearly three times the thickness of the femur of the largest Elephant. Its breadth is nearly half its entire length, and its head is united to the body of the bone by a neck of unusual shortness and strength, twenty-two inches in circumference. Its length is two feet four inches, and its circumference at the smallest part two feet two inches; and at the largest part, three feet two inches. Its body is also flattened; and by means of this flatness, expanded outwards to a degree of which Nature presents no other example. These peculiarities in the femur appear to be subservient to a double purpose: first, to give extraordinary strength by the shortness and solidity of all its proportions; and secondly, to afford compensation by its flatness outwards; for the debility which would otherwise have followed from the inward position of the sockets, (t,) by which the femur, (u,) articulates with the pelvis.

The two bones of the leg (x, y,) are also extremely short, and on a scale of solidity and strength, commensurate with that of the femur that rests upon them. This strength is much increased by their being united at both extremities; a union which is said by Cuvier to occur in no other animals except the Armadillo and Chlamyphorus; both of which are continually occupied in digging for their food.

The articulation of the leg with the hind foot is admirably contrived for supporting the enormous pressure of downward weight; the astragalus (z,) or great bone of the instep, being nine inches broad and nine inches high, is in due proportion to the lower extremity of the tibia, or leg bone, with which it articulates; and rests upon a heel bone, of the extraordinary length of seventeen inches, with a circumference of twenty-eight inches. This enormous bone, pressing on the ground, gives a firm bearing and solid support to the continuous accumulation of weight, which we have been tracing down from the pelvis through the thigh and leg: in fact the heel-bone occupies nearly one-half of the entire length of the hind-foot; the bones of the toes are all short, excepting the extreme joint, which forms an enormous claw-bone; larger than the largest of those in the fore-foot, measuring thirteen inches in circumference, and having within its sheath a core, ten inches long, for the support of the horny claw with which it was invested. The chief use of this large claw was probably to keep the hind-foot fixed steadily upon the ground.^[11]

Feet and legs thus heavily constructed, must have been very inefficient organs of rapid locomotion, and may consequently seem imperfect, if considered in relation to the ordinary functions of other quadrupeds; but, viewed as instruments adapted for supporting an almost stationary creature, of unusual weight, they claim our admiration equally with every other piece of animal mechanism, when its end and uses are understood. The perfection of any instrument can only be appreciated by looking to the work it is intended to perform. The hammer and anvil of an anchor smith, though massive, are neither clumsy nor imperfect; but bear the same proportionate relation to the work in which they are employed, as the light and fine tools of the watchmaker bear to the more delicate wheels of his chronometer.

Bony Armour.

Another remarkable character of the Megatherium, in which it approaches most nearly to the Armadillo, and Chlamyphorus, consists, in its hide having probably been covered with a bony coat of armour; varying from three fourths of an inch, to an inch and a half in thickness, and resembling the armour which covers these living inhabitants, of the same warm and sandy regions of South America. Fragments of this armour are represented at Pl. 5, Figs. 12, 13.^[12]

A covering of such enormous Weight, would have been consistent with the general structure of the Megatherium; its columnar hind-legs and colossal tail, were calculated to give it due support; and the strength of the loins and ribs, being very much greater than in the Elephant, seems to have been necessary for carrying so ponderous a cuirass as that which we suppose to have covered the body.^[13]

It remains to consider, of what use this cuirass could have been to the gigantic animal on which it probably was placed. As the locomotive organs of the Megatherium indicate very slow power of progression, the weight of a cuirass would have afforded little impediment to such tardy movements; its use was probably defensive, not only against the tusks and claws of beasts of prey, but also, against the myriads of insects, that usually swarm in such climates as those wherein its bones are found; and to which an animal that obtained its food by digging beneath a broiling sun, would be in a peculiar degree exposed. We may also conjecture it to have had a further use in the protection afforded by it to the back, and upper parts of the body; not only against the sun and rain, but against the accumulations of sand and dust, that might otherwise have produced irritation and diseased.^[14]

Conclusion.

We have now examined in detail the skeleton of an extinct quadruped of enormous magnitude; every bone of which presents peculiarities, that at first sight appear imperfectly contrived, but which become, intelligible when viewed in their relations to one another, and to the functions of the animal in which they occur.

The size of the Megatherium exceeds that of the existing Edentata, to which it is most nearly allied, in a greater degree than any other fossil animal exceeds its nearest living congeners. With the head and shoulders of a Sloth, it combined in its legs and feet, an admixture of the characters of the Ant-eater, the Armadillo, and the Chlamyphorus; it probably also still further resembled the Armadillo and Chlamyphorus, in being cased with a bony coat of armour. Its haunches were more than five feet wide, and its body twelve feet long and eight feet high; its feet were a yard in length, and terminated by most gigantic claws; its tail was probably clad in armour, and much larger than the tail of any other beast, among extinct or living terrestrial Mammalia. Thus heavily constructed and ponderously accoutered, it could neither run, nor leap, nor climb, nor burrow under the ground, and in all its Movements must have been necessarily slow; but what need of rapid locomotion to an animal, whose occupation of digging roots for food was almost stationary? and what need of speed for flight from foes, to a creature whose giant carcass was encased in an impenetrable cuirass, and who by a single pat of his paw, or lash of his tail, could in an instant have demolished the Couguar or the Crocodile? Secure within the panoply of his bony armour, where was the enemy that would dare encounter this Leviathan of the Pampas? or, in what more powerful creature can we find the cause that has effected the extirpation of his race?

His entire frame was an apparatus of colossal mechanism, adapted exactly to the work it had to do; strong and ponderous, in proportion as this work was heavy, and calculated to be the vehicle of life and enjoyment to a gigantic race of quadrupeds; which, though they have ceased to be counted among the living inhabitants of our planet, have, in their fossil bones, left behind them imperishable monuments of the consummate skill with which they were constructed. Each limb, and fragment of a limb, forming co-ordinate parts of a well-adjusted and perfect whole; and through all their deviations from the form and proportion of the limbs of other quadrupeds, affording fresh proofs of the infinitely varied, and inexhaustible contrivances of Creative Wisdom.

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SECTION III.

FOSSIL SAURIANS.

In those distant ages that elapsed during the formation of strata of the secondary series, so large a field was occupied by reptiles, referable to the order of Saurians, that it becomes an important part of our inquiry to examine the history and organization of these curious relics of ancient creations, which are known to us only in a fossil state. A task like this may appear quite hopeless to persons unaccustomed to the investigation of subjects of such remote antiquity; yet Geology, as now pursued, with the aid of comparative anatomy, supplies abundant evidence of the structure and functions of these extinct families of reptiles; and not only enables us to infer from the restoration of their skeletons, what may have been the external form of their bodies; but instructs us also as to their economy and habits, the nature of their food, and even of their organs of digestion. It further shows their relations to the then existing condition of the world, and to the other forms of organic life with which they were associated.

The remains of these reptiles bear a much greater resemblance to one another, than to those of any animals we discover in deposites preceding or succeeding the secondary series.^[15]

The species of fossil Saurians are so numerous, that we can only select a few of the most remarkable among them, for the purpose of exemplifying the prevailing conditions of animal life, at the periods when the dominant class of animated beings were reptiles; attaining, in many cases, a magnitude unknown among the living orders of that class, and which seems to have been peculiar to those middle ages of geological chronology, that were intermediate between the transition and tertiary formations.

During these ages of reptiles, neither the carnivorous nor lacustrine Mammalia of the tertiary periods had begun to appear; but the most formidable occupants, both of land and water, were Crocodiles, and Lizards; of various forms, and often of gigantic stature, fitted to endure the turbulence, and continual convulsions of the unquiet surface of our infant world.

When we see that so large and important a rang has been assigned to reptiles among the former population of planet, we cannot but regard with feelings of new and unusual interest, the comparatively diminutive existing orders of that most ancient family of quadrupeds, with the very name of which we usually associate a sentiment of disgust. We shall view them with less contempt, when we learn from the records of geological history, that there was a time when reptiles not only constituted the chief tenants and most powerful possessors of the earth, but extended their dominion also over the waters of the seas; and that the annals of their history may be traced back through thousands of years, antecedent to that latest point in the progressive stages of animal creation, when the first parents of the human race were called into existence.

Persons to whom this subject may now be presented for the first time, will receive, with much surprise, perhaps, almost with incredulity, such statements as are here advanced. It must be admitted, that they at first seem much more like the dreams of fiction and romance, than the sober results of calm and deliberate investigation; but to those who will examine the evidence of facts upon which our conclusions rest, there can remain no more reasonable doubt of the former existence of these strange and curious creatures, in the times and places we assign to them; than is felt by the antiquary, who, finding the catacombs of Egypt stored with the mummies of Men, and Apes, and Crocodiles, concludes them to be the remains of mammalia and reptiles, that have formed part of an ancient population on the banks of the Nile.

SECTION IV.

FOSSIL SAURIANS.

Nearly at the head of the surprising discoveries, which have been made relating to the family of Saurians, we may rank the remains of many extraordinary species, which inhabited the sea; and which present almost incredible combinations of form, and structure; adapting them for modes of life that do not occur among living reptiles. These remains are most abundant throughout the lias and oolite formations of the secondary series.^[16] In these deposites we find not only animals allied to Crocodiles, and nearly approaching to the Gavial of the Ganges; but also still more numerous gigantic Lizards, that inhabited the then existing seas and estuaries.

Some of the most remarkable of these reptiles have been arranged under the genus Ichthyosaurus, (or Fish Lizard,) in consequence of the partial resemblance of their vertebræ to those of fishes. (See Plate 1, Fig. 51, and Plates 7, 8, 9.) If we examine these creatures with a view to their capabilities of locomotion, and the means of offence and defence which their extraordinary structure afforded to them; we shall find combinations of form and mechanical contrivances which are now dispersed through various classes and orders of existing animals, but are no longer united in the same genus. Thus, in the same individual, the snout of a Porpoise is combined with the teeth of a Crocodile, the head of a Lizard with the Vertebræ of a fish, and the sternum of an Ornithorhynchus with the paddles of a Whale. The general outline of an Ichthyosaurus must have most nearly resembled the modern Porpoise, and Grampus. It had four broad feet, or paddles, (Pl. 7,) and terminated behind in a long and powerful tail. Some of the largest of these reptiles must have exceeded thirty feet in length.

There are seven or eight known species of the genus Ichthyosaurus, all agreeing with one another in the general principles of their construction, and the possession of those peculiar organs, in which I shall endeavour to point out the presence of mechanism and contrivance, adapted to their habits and state of life. As it will be foreign to our purpose to enter on details respecting species, I shall content myself with referring to the figures of the four most common forms (Plates 7, 8, 9.)^[17]

Head.

The head, which-in all animals forms the most important and characteristic part, (see Pl. 10, Figs. 1, 2,) at once shows that the Ichthyosauri were Reptiles, partaking partly of the characters of the modern Crocodiles, but more allied to Lizards. They approach nearest to Crocodiles in the form and arrangement of their teeth. The position of the nostril is not, as in Crocodiles, near the point of the snout; it is set, as in Lizards, near the anterior angle of the orbit of the eye. The most extraordinary feature of the head, is the enormous magnitude of the eye, very much exceeding that of any living animal.^[18] The expansion of the jaws must have been prodigious; their length in the larger species, (Ichthyosaurus Platyodon,) sometimes exceeding six feet; the voracity of the animal was doubtless in proportion to its powers of destruction. The neck was short, as in fishes.

Teeth.

The teeth of the Ichthyosaurus (Pl. II, B, C,) are conical, and much like those of the Crocodiles, but considerably more numerous, amounting in some cases to a hundred and eighty; they vary in each species; they are not enclosed in deep and separate sockets, as the teeth of Crocodiles, but are ranged in one long continuous furrow, (Pl. II, B, C,) of the maxillary bone, in which the rudiments of a separation into distinct alveoli may be traced in slight ridges extending between the teeth, along the sides and bottom of the furrow. The contrivance by which the new tooth replaces the old one, is very nearly the some in the Ichthyosauri as in the Crocodiles (Pl. II, A, B, C;) in both, the young tooth begins its growth at the base of the old tooth, where, by pressure on one side, it causes first a partial absorption of the base, and finally a total removal of the body of the older tooth, which it is destined to replace.^[19]

As the predaceous habits of the Ichthyosauri exposed them, like modern Crocodiles, to frequent loss of their teeth, an abundant provision has in each case been made for their continual renewal.

Eyes.

The enormous magnitude of the eye of the Ichthyosaurus (Pl. 10, Fig. I, 2,) is among the most remarkable peculiarities in the structure of this animal. From the quantity of light admitted in consequence of its prodigious size, it must have possessed very great powers of vision; we have also evidence that it had both microscopic and telescopic properties. We find on the front of the orbital cavity in which this eye was lodged, a circular series of petrified thin bony plates, ranged around a central aperture, where once was placed the pupil; the form and thickness of each of these plates very much resembles that of the scales of an artichoke (Pl. 10, Fig. 3.) This compound circle of bony plates, does not occur in fishes; but is found in the eyes of many birds,^[20] as well as of Turtles, Tortoises, and Lizards; and in a less degree in Crocodiles. (Pl. 10, Figs. 4, 5, 6.)

In living animals these bony plates are fixed in the exterior or sclerotic coat of the eye, and vary its scope of action, by altering the convexity of the cornea: by their retraction they press forward the front of the eye and convert it into a microscope; in resuming their position, when the eye is at rest, they convert it into a telescope. The soft parts of the eyes of the Ichthyosauri have of course entirely perished; but the preservation of this curiously constructed hoop of bony plates, shows that the enormous eye, of which they formed the front, was an optical instrument of varied and prodigious power, enabling the Ichthyosaurus to descry its prey at great or little distances, in the obscurity of night, and in the depths of the sea; it also tends to associate the animal, in which it existed, with the family of Lizards, and exclude it from that of fishes.^[21]

A further advantage resulting from this, curious apparatus of bony plates, was to give strength to the surface of so large an eye-ball, enabling it the better to resist the pressure of deep water, to which it must often have been exposed; it would also have protected this important organ from injury by the waves of the sea, to which an eye, sometimes larger than a man's head, must frequently have been subject, when the nose was brought to the surface, for the necessary purpose of breathing air: the position of the nostrils, close to the anterior angle of the eye, rendered it impossible for the Ichthyosaurus to breathe without raising its eye to the surface of the water.

Jaws.

The Jaws of the Ichthyosauri, like those of Crocodiles and Lizards, which are all more or less elongated into projecting beaks, are composed of many thin plates, so arranged as to combine strength with elasticity and lightness, in a greater degree than could have been effected by single bones, like those in the jaws of Mammalia. It is obvious that an under jaw so slender, and so much elongated as that of a Crocodile or Ichthyosaurus, and employed in seizing and retaining the large and powerful animals which formed their prey, would have been comparatively weak and liable to fracture if composed of a single bone. Each side of the lower jaw was therefore made up of six separate pieces, set together in a manner that will be best understood by reference to the Figures in Pl. 11.^[22]

This contrivance in the lower jaw, to combine the greatest elasticity and strength, with the smallest weight of materials, is similar to that adopted in binding together several parallel plates of elastic wood, or steel, to make a crossbow; and also in setting together thin plates of steel in the springs of carriages. As in the carriage spring, or compound bow, so also in the compound jaw of the Ichthyosaurus, the plates are most numerous and strong, at the parts where the greatest strength is required to be exerted; and are thinner, and fewer, towards the extremities, where the service to be performed is less severe. Those who have witnessed the shock given to the head of a Crocodile, by the act of snapping together its thin long jaws, must have seen how liable to fracture the lower jaw would be, were it composed of one bone only on each side: a similar inconvenience would have attended the same simplicity of structure in the jaw of the Ichthyosaurus. In each case, therefore, the splicing and bracing together of six thin flat bones of unequal length, and of varying thickness, on both sides of the lower jaw, affords compensation for the weakness and risk of fracture, that would otherwise have attended the elongation of the snout.

Mr. Conybeare points out a further beautiful contrivance in the lower jaw of the Ichthyosaurus, analogous to the cross bracings lately introduced in naval architecture, (see Pl. 11, Fig. 2.)^[23]

Vertebræ.

The vertebral column in the Ichthyosaurus was composed of more than one hundred joints; and although united to a head nearly resembling that of a Lizard, assumed, in the leading principles of its construction, the character of the vertebræ of fishes. As this animal was constructed for rapid motion through the sea, the mechanism of hollow vertebræ, which gives facility of movement in water to fishes, was better calculated for its functions than the solid vertebra of Lizards and Crocodiles^[24] (See Plate 12, A. and B.) This hollow conical form would be inapplicable to the vertebrae of land quadrupeds, whose back, being nearly at right angles to the legs, requires a succession of broad and nearly iiat qrfaces, which press with considerable weight against each other. It is quite certain, therefore, that such large and bulky creatures as the Ichthyosauri, having their vertebræ constructed after the manner of fishes, had they been furnished with legs instead of paddles, could not have moved on land without injury to their backs.^[25]

Ribs.

The ribs were slender, and most of them bifurcated at the top: they were also continuous along the whole vertebral column, from the head to the pelvis, (see Plates 7, 8, 9); and in this respect agree with the structure of modern Lizards. A considerable number of them were united in front across the chest: their mode of articulation may be seen in Pl. 14. The ribs of the right side were united to those of the left, by intermediate bones, analogous to the cartilaginous intermediate and sternal portions of the ribs in Crocodiles; and to the bones which, in the Plesiosaurus, form what Mr. Conybeare has called the sterno-costal arcs. (See Pl. 17.) This structure was probably subservient to the purpose of introducing to their bodies an unusual quantity of air; the animal by this means being enabled to remain long beneath the water, without rising to the surface for the purpose of breathing.^[26]

Sternum.

To a marine animal that breathed air, it was essential to possess an apparatus whereby its ascent and descent in the water may have been easily accomplished; accordingly we find such an apparatus, constructed with prodigious strength, in the anterior paddles of the Ichthyosaurus; and in the no less extraordinary combination of bones that formed the sternal arch, or that part of the chest, on which these paddles rested. Pl. 12, Fig. 1.

It is a curious fact, that the bones composing the sternal arch are combined nearly in the same manner as in the Ornithorhynchus^[27] of New Holland; which seeks its food at the bottom of lakes and rivers, and is obliged, like the Ichthyosaurus, to be continually rising to the surface to breathe air.^[28]

Here then we have a race of animals that became extinct at the termination of the secondary series of geological formations, presenting, in their structure, a series of contrivances, the same in principle, with those employed at the present day to effect a similar purpose in one of the most curiously constructed aquatic quadrupeds of New Holland.^[29]

Paddles.

In the form of its extremities, the Ichthyosaurus deviates from the Lizards, and approaches the Whales. A large animal, moving rapidly through the sea, and breathing air, must have required great modifications of the fore-leg and foot of the Lizard, to fit it for such cetaceous habits. The extremities were to be converted into fins instead of feet, and as such we shall find them to combine even a still greater union of elasticity with strength, than is presented by the fin or paddle of the Whale. Plate 12, Fig. 1, shows the short and strong bones of the arm (e,) and those of the fore-arm (f, g;) and beyond these the series of polygonal bones that made up the phalanges of the fingers. These polygonal bones vary in number in different species, in some exceeding one hundred; they differ also in form from the phalanges both of Lizards and Whales: and derive, from their increase of number, and change of dimensions, an increase of elasticity and power. The arm and hand thus converted into an elastic oar or paddle, when covered with skin, must have much resembled externally the undivided paddle of a Porpoise or Whale. The position also of the paddles on the anterior part of the body was nearly the same; to these were superadded posterior extremities, or hind fins, which are wanting in the cetacea, and which possibly make compensation for the absence of their flat horizontal tail: these hind paddles in the Ichthyosaurus are nearly by one half smaller than the anterior paddles.^[30]

Mr. Conybeare remarks, with his usual acumen, that "the reasons of this variation from the proportions of the posterior extremities of quadrupeds in general, are the same which lead to a similar diminution of the analogous parts in Seals, and their total disappearance in the cetacea, namely, the necessity of placing the centre of the organs of motion, when acting laterally, before the centre of gravity. For the same reason, the wings of birds are placed in the fore part of their body, and the centre of the moving forces given to ships by their sails, and to steam-boats by their paddles, is similarly placed. The great organ of motion in fishes, the tail, is indeed posteriorly placed, but this by its mode of action generates a vis a tergo, which impels the animal straight forwards, and does not therefore operate under the same conditions with organs laterally applied." G. T. V. 5, p. 579.

I shall conclude this detailed review of the peculiarities of one of the most curious, as well as the most ancient, among the many genera of extinct reptiles presented to us by Geology, with a few remarks on the final causes of those deviations from the normal structure of its proper type, the Lizard; under which the Ichthyosaurus combines in itself the additional characters of the fish, the Whale, and Ornithorhynchus. As the form of vertebræ by which it is associated with the class of fishes, seems to have been introduced for the purpose of giving rapid motion in the water to a Lizard inhabiting the element of fishes; so the further adoption of a structure in the legs, resembling the paddles of a Whale, was superadded in order to convert these extremities into powerful fins. The still further addition of a furcula and clavicles, like those of the Ornithorhynchus, offers a third and not less striking example of selection of contrivances, to enable animals of one class to live in the element of another class.

If the laws of co-existence are less rigidly maintained in the Ichthyosaurus, than in other extinct creatures which we discover amid the wreck of former creations, still these deviations are so far from being fortuitous, or evidencing imperfection, that they present examples of perfect appointment and judicious choice, pervading and regulating even the most apparently anomalous aberrations.

Having the vertebræ of a fish, as instruments of rapid progression; and the paddles of a Whale, and sternum of an Ornithorhynchus, as instruments of elevation and depression; the reptile Ichthyosaurus united in itself a combination mechanical contrivances, which are now distributed among three distinct classes of the animal kingdom. If; for the purpose of producing vertical movements in the water, the sternum of the living Ornithorhynchus assumes forms and combinations that occur but in one other genus of Mammalia, they are the same that co-existed in the sternum of the Ichthyosaurus of the ancient world; and thus, at points of time, separated from each other by the intervention of incalculable ages, we find an identity of objects effected by instruments so similar, as to leave no doubt of the unity of the design in which they all originated.

It was a necessary and peculiar function in the economy of the fish-like Lizard of the ancient seas, to ascend continually to the surface of the water in order to breathe air, and to descend again in search of food; it is a no less peculiar function in the Duck-billed Ornithorhynchus of our own days, to perform a series of similar movements in the lakes and rivers of New Holland.

The introduction to these animals, of such aberrations from the type of their respective orders to accommodate deviations from the usual habits of these orders, exhibits a union of compensative contrivances, so similar in their relations, so identical in their objects, and so perfect in the adaptation of each subordinate part, to the harmony and perfection of the whole; that we cannot but recognise throughout them all, the workings of one and the same eternal principle of Wisdom and Intelligence, presiding from first to last over the total fabric of Creation.

SECTION V.

INTESTINAL STRUCTURE OF ICHTHYOSAURUS AND FOSSIL FISHES.

From the teeth and organs of locomotion, we come next to consider those of digestion in the Ichthyosaurus. If there be any point in the structure of extinct fossil animals, as to which it should have seemed hopeless to discover any kind of evidence, it is the form and arrangement of the intestinal organs; since these soft parts, though of prime importance in the animal economy, yet being suspended freely within the cavity of the body, and unconnected with the skeleton, would leave no traces whatever upon the fossil bones.

It is impossible to have seen the large apparatus of teeth, and strength of jaws, which we have been examining in the Ichthyosauri, without concluding that animals furnished with such powerful instruments of destruction, must have used them freely in restraining the excessive population of the ancient seas. This inference has been fully confirmed by the recent discovery within their skeletons, of the half digested remains of fishes and reptiles, which they had devoured, (see Pl. 13, 14,) and by the further discovery of Coprolites, (see Pl. 15,) i. e. of fœcal remains in a state of petrifaction, dispersed through the same strata in which these skeletons are buried. The state of preservation of these very curious petrified bodies is often so perfect, as to indicate not only the food of the animals from which they were derived, but also the dimensions, form, and structure of their stomach, and intestinal canal.^[31]

On the shore at Lyme Regis, these Coprolites are so abundant, that they lie in some parts of the lias like potatoes scattered in the ground; still more common are they in the lias of the Estuary of the Severn, where they are

similarly disposed in strata of many miles in extent, and mixed so abundantly with teeth and rolled fragments of the bones of reptiles and fishes, as to show that this region, having been the bottom of an ancient sea, was for a long period the receptacle of the bones and fœcal remains of its inhabitants. The occurrence of Coprolites is not, however, peculiar to the places just mentioned; they are found in greater or less abundance throughout the lias of England; they occur also in strata, of all ages that contain the remains of carnivorous reptiles, and have been recognised in many and distant regions both of Europe and America.^[32]

The certainty of the origin of these Coprolites is established by their frequent presence in the abdominal region of fossil skeletons of Ichthyosauri found in the lias of Lyme Regis. One of the most remarkable of these is represented in Pl. 13; the coprolitic matter loaded with fish-scales, within the ribs of these and similar specimens, is identical in appearance and chemical composition with the insulated

coprolites that occur in the same strata with the skeletons.^[33]

The preservation of such fœaecal matter, and its conversion to the state of stone, result from the imperishable nature of the phosphate of lime, of which both bones, and the products of digested bones are equally composed.

The skeleton of another Ichthyosaurus in the Oxford Museum, from the lias at Lyme Regis, (Pl. 14) shows a large mass of fish scales, chiefly referable to they Pholidophorus, limbatus,^[34] intermixed with coprolite throughout the entire region of the ribs; this mass is overlaid by many ribs, and although, in some degree perhaps, extended by pressure, it shows that the length of the stomach was nearly co-extensive with the trunk.

Among living voracious reptiles we have examples of stomachs equally capacious; we know that whole human bodies have been found within the stomachs of large Crocodiles; we know also, from the form of their teeth, that the Ichthyosauri, like the Crocodiles, must have gorged their prey entire; and when we find, imbedded in Coprolites derived from the larger Ichthyosauri, bones of smaller Ichthyosauri, of such dimensions, (see Pl. 15, Fig. 18. And Geol. Trans. 2, S. vol. iii, Pl. 29, Figs, 2, 3, 4, 5,) that the individuals from which they were derived, must have measured several feet in length; we infer that the stomach of these animals formed a pouch, or sac, of prodigious size, extending through nearly the entire cavity of the body, and of capacity duly proportioned to the jaws and, teeth with which it co-operated.

Spiral Disposition of Small Intestines.

As the more solid parts of animals alone, are usually susceptible of petrifaction, we cannot demonstrate by direct evidence the form and size of the small intestines of the Ichthyosauri, but the contents of these viscera are preserved in such perfection in a fossil state, as to afford circumstantial evidence that the bowels in which they were moulded, were formed in a manner resembling the spiral intestines of some of the swiftest and most voracious of our modern fishes.

We shall best understand the structure of these intestines by examining the corresponding organs of Sharks and Dog-fish, animals not less peculiarly rapacious among the inhabitants of our modern seas, than the Ichthyosauri were in those early periods to which our considerations are carried back. We find in the intestines of these fishes, Pl. 15, Figs. 1, and 2,) and also in those of Rays, an arrangement resembling that of the interior of an Archimedes screw, admirably adapted to increase the extent of internal surface for the absorption of nutriment from the food, during its passage through a tube containing within it a continuous spiral fold, coiled in such a manner, as to afford the greatest possible extent of surface in the smallest space. A similar contrivance is shown by the Coprolites to have existed in the Ichthyosaurus. See Pl. 15, Figs. 3, 4, 6.^[35]

Impressions of the Mucous Membrane on Coprolites.

Besides the spiral structure and consequent shortness of the small intestine, we have additional evidence to show even the form of the minute vessels and folds of the mucous membrane, by which it was lined, This evidence consists in a series of vascular impressions and corrugations on the surface of the Coprolite, which it could only have received during its passage through the windings of this flat tube.^[36] Specimens thus marked are engraved at Pl. 15, Figs. 3, 5, 7, 10, 12, 13, 14.

If we attempt to discover a final cause for these curious provisions in the bowels of the extinct reptile inhabitants of the seas of a former world, we shall find it to be the same that explains the existence of a similar structure in the modern voracious tribes of Sharks and Dog-fish.^[37]

As the peculiar voracity of all these animals required the stomach to be both large and long, there would remain but little space for the smaller viscera; these are therefore reduced, as we have seen, nearly to the state of a flattened tube, coiled like a corkscrew around itself; their bulk is thus materially diminished, whilst the amount of absorbing surface remains almost the same, as if they had been circular. Had a large expansion of intestines been superadded to the enormous stomach and lungs of the Ichthyosaurus. the consequent enlargement of the body would have diminished the power of progressive motion, to the great detriment of an animal which depended on its speed for the capture of its prey.

The above facts which we have elicited from the coprolitic remains of the Ichthyosauri, afford a new and curious contribution to our knowledge both of the anatomy and habits of the extinct inhabitants of our planet. We have found evidence which enables us to point out the existence of beneficial arrangements and compensations, even in those perishable, yet important parts which formed their organs of digestion. We have ascertained the nature of their food, and the form and structure of their intestinal canal; and have traced the digestive organs through three distinct stages of descent, from a large and long stomach, through the spiral coils of a compressed ileum, to their termination in a cloaca; from which the Coprolites descended into the mud of the nascent lias. In this lias they have been interred during countless ages, until summoned from its deep recesses by the labours of the Geologist, to give evidence of events that passed at the bottom of the ancient seas, in ages long preceding the existence of man.

Intestinal Structure of Fossil Fishes.

Discoveries have recently been made of Coprolites derived from fossil fishes. Mr. Mantell has found them within the body of the Macropoma Mantellii, from the chalk of Lewes, placed in contact with the long stomach of this voracious fish: the coats of its stomach are also well preserved.^[38] Miss Anning also has discovered them within the bodies of several species of fossil fish, from the lias at Lyme Regis. Dr. Hibbert has shown that the strata of freshwater limestone, in the lower region of the coal formation, at Burdie House, near Edinburgh, are abundantly interspersed with Coprolites, derived from fishes of that early era; and Sir Philip Egerton has found similar fœcal remains, mixed with scales -of the Megalichthys, and fresh water shells, in the coal formation of Newcastle-under-Lyne. In 1832, Mr. W. C. Trevelyan recognised Coprolites in the centre of nodules of clay ironstone, that abound in a low cliff composed of shale, belonging to the coal formation at Newhaven, near Leith. I visited the spot, with this gentleman and Lord Greenock, in September, 1834, and found these nodules strewed so thickly upon the shore that a few minutes sufficed to collect more specimens than I could carry; many of these contained a fossil fish, or fragment of a plant, but the greater number had for their nucleus, a Coprolite, exhibiting an internal spiral structure; they were probably derived from voracious fishes, whose bones are found in the same stratum. These nodules take a beautiful polish, and have been applied by the lapidaries of Edinburgh to make tables, letter presses, and ladies ornaments, under the name of Beetle stones, from their supposed insect origin. Lord Greenock has discovered, between the laminæ of a block of coal, from the neighbourhood of Edinburgh, a mass of petrified intestines distended with Coprolite, and surrounded with the scales of a fish, which Professor Agassiz refers to the Megalichthys.

This distinguished naturalist has recently ascertained that the fossil worm-like bodies, so abundant in the lithographic slate of Solenhofen, and described by Count Münster in the Petrefacten of Goldfuss, under the name of Lumbricaria, are either the petrified intestines of fishes, or the contents of Qtheir intestines, still retaining the form of the tortuous tube in which they were lodged. To these remarkable fossils he has given the name of Cololites. (Pl. 15', is copied from one of a series that are engraved in Goldfuss, Petrefacten, Pl. 66.) He has also found similar tortuous petrifactions within the abdominal cavity of fossil fishes. belonging to several species of the genus Thrissops and Leptolepis, occupying the ordinary position of the intestines between the ribs.^[39] (See Agassiz Poissons Fossiles, liv. 2, Appendix, p. 15.)

It is probable that to many persons inexperienced in anatomy, any kind of information on a subject so remote, and apparently so inaccessible, as the intestinal structure of an extinct reptile or fossil fish, may at first appear devoid of the smallest possible importance; but it assumes a character of high value, in the investigation of the proofs of creative wisdom and design, that ans unfolded by the researches of Geology; and supplies a new link to that important chain, which connects the lost races that formerly inhabited our planet, with a species that are actually living and moving around ourselves.^[40] The systematic recurrence, in animals of, such distant eras, of the same contrivances, similarly disposed to effect similar purposes, with analogous adaptations to peculiar conditions of existence, shows that they all originated in the same Intelligence.

When we see the body of an Ichthyosaurus still containing the food it had eaten just before its death, and its ribs still surrounding the remains of fishes, that were swallowed ten thousand, or more than ten times ten thousand year; ago, all these vast intervals seem annihilated, time altogether disappears, and we are almost brought into as immediate contact with events of immeasurably distant periods; as with the affairs of yesterday.

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SECTION VI.

PLESIOSAURUS.^[41]

We come next to consider a genus of extinct animals, nearly allied in structure to the Ichthyosaurus, and co-extensive with it through the middle ages of our terrestrial history. The discovery of this genus forms one of the most important additions that Geology has made to comparative anatomy. It is of the Plesiosaurus, that Cuvier asserts the structure to have been the most heteroclite, and its characters altogether the most monstrous, that have been yet found amid the ruins of a former world.^[42] To the head of a Lizard, it united the teeth of a Crocodile; a neck of enormous length, resembling the body of a Serpent: a trunk and tail having the proportions of an ordinary quadruped, the ribs of a Chameleon, and the paddles of a Whale. Such are the strange combinations of form and structure in the Plesiosaurus—a genus, the remains of which, after interment for thousands of years amidst the wreck of millions of extinct inhabitants of the ancient earth, are at length recalled to light by the researches of the Geologist, and submitted to our examination, in nearly as perfect a state as the bones of species that are now existing upon the earth.

The Plesiosauri appear to have lived in shallow seas and estuaries, and to have breathed air like the Ichthyosauri, and our modern Cetacea. We are already acquainted with five or six species, some of which attained a prodigious size and length; but our present observations will be chiefly limited to that which is the best known, and perhaps the most remarkable of them all, viz. the P. Dolichodeirus.^[43]

Head.^[44]

The head of the P. Dolichodeirus exhibits a combination of the characters of the Ichthyosaurus, the Crocodile, and the Lizard, but most nearly approaches to the latter. It agrees with the Ichthyosaurus in the smallness of its nostrils, and also in their position near the anterior angle of the eye; it resembles the Crocodile, in having the teeth lodged in distinct alveoli; but differs from both, in the form and shortness of its head, many characters of which approach closely to the Iguana.^[45]

Neck.

The most anomalous of all the characters of P. Dolichodeirus is the extraordinary extension of the neck, to a length almost equalling that of the body and tail together, and surpassing in the number of its vertebræ (about thirty-three) that of the most long-necked bird, the Swan: it thus deviates in the greatest degree from the almost universal law, which limits the cervical vertebræ of quadrupeds to a very small number. Even in the Camelopard. the Camel, and Lama, their number is uniformly seven. In the short neck of the Cetacea the type of this number is maintained. In Birds it varies from nine to twenty-three; and in living Reptiles from three to eight.^[46] We shall presently find in the habits of the Plesiosaurus a probable cause for this extraordinary deviation from the normal character of the Lizards.

Back and Tail.

The vertebræ of the back were not disposed in hollow cones, like those of fishes, but presented to each other nearly flat surfaces, giving to the column a stability, like that which exists in the back of terrestrial quadrupeds. The articulating processes, also, were locked into one another in such a manner as to give strength, rather than that peculiar kind of flexibility, which admitted of the same quick progressive motion in the Ichthyosauri that we find in fishes: but as rapid motion was incompatible with the structure of the other parts of the Plesiosaurus, the combination of strength, rather than of speed with flexibility, was more important.

The tail being comparatively short, could not have been used like the tail of fishes, as an instrument of rapid impulsion in a forward direction; but was probably employed more as a rudder, to steer the animal when swimming on the surface, or to elevate or depress it in ascending and descending through the water. The same consequence as to slowness of motion would follow from the elongation of the neck to so great a distance in front of the anterior paddles. The total number of vertebræ in the entire column was about ninety. From all these circumstances we may infer that this animal, although of considerable size, had to seek its food, as well as its safety, chiefly by means of artifice and concealment.

Ribs.^[47]

The ribs are composed of two parts, one vertebral and one ventral; the ventral portions of one side, (Pl. 18, 3, b,) uniting with those on the opposite side by an intermediate transverse bone, (a, c,) so that each pair of ribs encircled the body with a complete belt, made up of five parts.^[48] Cuvier observes that the similarity of this structure to that of the ribs of Chameleons and two species of Iguana, (Lacerta Marmorata, Lin. and Anolius, Cuvier,) seems to show that the lungs of the Plesiosaurus Dolichodeirus, (as in these three subgenera of living Saurians,) were very large; and possibly that the colour of its skin also was changeable, by the varied intensity of its inspirations.^[49] Oss. Foss. Vol. V. Pt. 2. p. 280.

This hypothesis of Cuvier is but conjectural, respecting the power of the Plesiosaurus to change the colour of its skin; and to the inexperienced in comparative anatomy, it may seem equally conjectural, to deduce any other conclusions respecting such perishable organs as the lungs, from the discovery of peculiar contrivances, and unusual apparatus in the ribs; yet we argue on similar grounds, when from the form and capabilities of these fossil ribs, we infer that they were connected, as in the Chameleon, with vast and unusual powers of expansion and contraction in the lungs; and when, on finding the ribs and wood-work of a worn-out bellows, near the ruins of a blacksmith's forge, we conclude that these more enduring parts of the frame of this instrument, have been connected, with a proportion able expansion of leather.

The compound character of the ribs, probably also gave to the, Plesiosaurus the same power of compressing air within its lungs, and in that state taking it to the bottom, which we have considered as resulting from the structure of the sterno-costal apparatus of the Ichthyosauri.

Extremeties.^[50]

As the Plesiosaurus breathed air, and was therefore obliged to rise often to the surface for inspiration, this necessity was met by an apparatus in the chest and pelvis, and in the bones of the arms and legs, enabling it to ascend and descend in the water after the manner of the Ichthyosauri and Cetacea; accordingly the legs were converted into paddles, longer and more powerful than those of the Ichthyosaurus, thus compensating for the comparatively small assistance which it could have derived from its tail.^[51]

Comparing them extremities with those of other vertebrated animals we trace a regular series of links and gradations, from the corresponding parts of the highest mammalia, to their least perfect form in the fins of fishes. In the fore paddle of the Plesiosaurus, we have all the essential parts of the fore leg of a quadruped, and even of a human arm; first the scapula, next the humerus, then the radius and ulna, succeeded by the bones of the carpus and metacarpus, and these followed by five fingers, each composed of a continuous series of phalanges. (See Pl. 16, 17, 19.) The hind paddle also offers precisely the same analogies to the leg and foot of the Mammalia; the pelvis and femur are succeeded by a tibia and fibula, which articulate with the bones of the tarsus and metatarsus, followed by the numerous phalanges of five long toes.

From the consideration of all its characters, Mr. Conybeare has drawn the following inferences with respect to the habits of the Plesiosaurus Dolichodeirus, "That it was aquatic is evident, from the form of its paddles; that it was marine is almost equally so, from the remains with which it is universally associated; that it may have occasionally visited the shore, the resemblance of its extremities to those of the Turtle may lead us to conjecture; its motion however must have been very awkward on land; its long neck must have impeded its progress through the water; presenting a striking contrast to the organization which so admirably fits the Ichthyosaurus to cut through the waves. May it not therefore be concluded (since, in addition to these circumstances, its respiration must have required frequent access of air,) that it swam upon or near the surface; arching back its long neck like the swan, and occasionally darting it down at the fish which happened to float within its reach. It may perhaps have lurked in shoal water along the coast, concealed among the sea-weed, and raising its nostrils to a level with the surface from a considerable depth, may have found a secure retreat from the assaults of dangerous enemies; while the length and flexibility of its neck may have compensated for the want of strength in its jaws, and its incapacity for swift motion through the water, by the suddenness and agility of the attack which they enabled it to make on every animal fitted for its prey, which came within its reach."—Geol. Trans. N. S. vol. i. part ii. p. 388.

We began our account of the Plesiosaurus with quoting the high authority of Cuvier, for considering it as one of the most anomalous and monstrous productions of the ancient systems of creation; we have seen in proceeding through our examination of its details, that these apparent anomalies consist only in the diversified arrangement, and varied proportion, of parts fundamentally the same as those that occur in the most perfectly formed creatures of the present world.

Pursuing the analogies of construction, that connect the existing inhabitants of the earth with those extinct genera and species which preceded the creation of our race, we find an unbroken chain of affinities pervading the entire series of organized beings and connecting all past and present forms of animal existence by close and harmonious ties. Even our own bodies, and some of their most important organs are brought into close and direct comparison with those of reptiles, which, at first sight, appear the most monstrous productions of creation; and in the very hand and fingers with which we write their history, we recognise the type of the paddles of the Ichthyosaurus and Plesiosaurus.

Extending a similar comparison through the four great classes of vertebral animals, we find in each species a varied adaptation of analogous parts, to the different circumstances and conditions in which it was intended to be placed. Ascending from the lower orders, we trace a gradual advancement in structure and office, till we arrive at those whose functions are the most exalted: thus, the tin of the fish becomes the paddle of the reptile Plesiosaurus and Ichthyosaurus; the same organ is converted into the wing of the Pterodactyle, the bird and bat; it becomes the fore-foot, or paw, in quadrupeds that move upon the land, and attains its highest consummation in the arm and hand of rational man.

I will conclude these observations in the words and with the feelings of Mr. Conybeare, which must be in unison with those of all who had the pleasure to follow him through his masterly investigations of this curious subject, from which great part of our information respecting the genus Plesiosaurus has been derived:

"To the observer actually engaged in tracing the various links that bind together the chain of organized beings, and struck at every instant by the development of the most beautiful analogies, almost every detail of comparative anatomy, however minute, acquires an interest, and even a charm; since he is continually presented with fresh proof of the great general law, which Scarpa himself; one of its most able investigators, has so elegantly expressed: 'Usque adeo natura, una eadem semper atque multiplex, disparibus etiam formis effectus pares, admirabili quadam varietatum simplicitate conciliate.'"

SECTION VII.

MOSOSAURUS, OR GREAT ANIMAL OF MAESTRICHT.

The Mosasaurus has been long known by the name of the great animal of Maestricht, occurring near that city, in the calcareous freestone which forms the most recent deposite of the cretaceous formation, and contains Ammonites, Belemnites, Hamites, and many other shells belonging to the chalk, mixed with numerous remains of marine animals that are peculiar to it self. A nearly perfect head of this animal was discovered in 1780, and is now in the Museum at Paris. This celebrated head during many years baffled all the skill of Naturalists; some considered it to be that of a Whale, others of a Crocodile; but its true place in the animal kingdom was first suggested by Adrian Camper, and at length confirmed by Cuvier. By their investigations it is proved to have been a gigantic marine reptile, most nearly allied to the Monitor.^[52] The geological epoch at which the Mosasaurus first appeared, seems to have been the last of the long series, during which the oolitic and cretaceous groups were in process of formation. In these periods the inhabitants of our planet seem to have been principally marine, and some of the largest creatures were Saurians of gigantic stature, many of them, living in the sea, and controlling the excessive increase of the then existing tribes of fishes.

From the lias upwards, to the commencement of the chalk formation, the Ichthyosauri and Plesiosauri were the tyrants of the ocean; and just at the point of time when their existence terminated, during the deposition of the chalk, the new genus Mosasaurus appears to have been introduced, to supply for a while their place and office,^[53] being itself destined in its turn to give place to the Cetacea of the tertiary periods. As no Saurians of the present world are inhabitants of the sea, and the most powerful living representatives of this order, viz. the Crocodiles, though living chiefly in water, have recourse to stratagem rather than speed, for the capture of their prey, it may not be unprofitable to examine the mechanical contrivances, by which a reptile, most nearly allied to the Monitor, was so constructed, as to possess the power of moving in the sea, with sufficient velocity to overtake and capture such large and powerful fishes, as from the enormous size of its teeth and jaws, we may conclude it was intended to devour.

The head and teeth, (Pl. 20.) point out the near relations of this animal to the Monitors; and the proportions maintained throughout all the other parts of the skeleton, warrant the conclusion that this monstrous Monitor of the ancient deep was five and twenty feet in length, although the longest of its modern conveners does not exceed five feet. The head here represented measures four feet in length, that of the largest Monitor does not exceed five inches. The most skilful Anatomist would be at a loss to devise a series of modifications, by which a Monitor could be enlarged to the length and bulk of a Grampus,^[54] and at the same time be fitted to move with strength and rapidity through the waters of the sea; yet in the fossil before us, we shall find the genuine characters of a Monitor maintained throughout the whole skeleton, with such deviations only as tended to fit the animal for its marine existence.

The Mosasaurus had scarcely any character in common with the Crocodile, but resembled the Iguanas, in having an apparatus of teeth fixed on the pterygoid bone, (Pl. 20, k.) and placed in the roof of its mouth, as in many serpents and fishes, where they act as barbs to prevent the escape of their prey.^[55]

The other parts of the skeleton follow the character indicated by the head. The vertebræ are all concave in front, and convex behind; being fitted to each other by a ball and socket joint, admitting easy and universal flexion. From the centre of the back to the extremity of the tail, they are destitute of articular apophyses, which are essential to support the back of animals that move on land: in this respect, they agree with the vertebræ of Dolphins, and were calculated to facilitate the power of swimming; the vertebræ of the neck allowed to that part also more flexibility than in the Crocodiles.

The tail was flattened on each side, but high and deep in the vertical direction, like the tail of a Crocodile; forming at straight oar of immense strength to propel the body by horizontal movements, analogous to those of skulling. Although the number of caudal vertebræ was nearly the same as in the Monitor, the proportionate length of the tail was much diminished by the comparative shortness of the body of each vertebræ; the effect of this variation being to give strength to a shorter tail as an organ for swimming; and a rapidity of movement, which would have been unattainable by the long and slender tail of the Monitor, which assists that animal in climbing. There is a further provision to give strength to the tail, by the chevron bones being soldered to the body of each vertebra, as in fishes.

The total number of vertebræ was one hundred and thirty-three, nearly the same as in the Monitors, and more than double the number of those in the Crocodiles. The ribs had a single head, and were round, as in the family of Lizards. Of the extremities, sufficient fragments have been found to prove that the Mosasaurus, instead of legs, had four large paddles, resembling those of the Plesiosaurus and the Whale: one great use of these was probably to assist in raising the animal to the surface, in order to breathe, as it apparently had not the horizontal tail, by means of which the Cetacea ascend for this purpose. All these characters unite to show that the Mosasaurus was adapted to live entirely in the water, and that although it was of such vast proportions compared with the living genera of these families, it formed a link intermediate between the Monitors and the Iguanas. However strange it may appear to find its dimensions so much exceeding those of any existing Lizards, or to find marine genera in the order of Saurians, in which there exists at this time no species capable of living in the sea; it is scarcely less strange than the analogous deviations in the Megalosaurus and Iguanodon, which afford examples of still greater expansion of the type of the Monitor and Iguana, into colossal forms adapted to move upon the land. Throughout all these variations of proportion, we trace the persistence of the same laws, which regulate the formation of living genera, and from the combinations of perfect mechanism that have, in all times, resulted from their operation, we infer the perfection of the wisdom by which all this mechanism was designed, and the immensity of the power by which it has ever been upheld.

Cuvier asserts of the Mosasaurus that before he had seen a single vertebra, or a bone of any of its extremities, he was enabled to announce the character of the entire skeleton, from the examination of the jaws and teeth alone, and even from a single tooth. The power of doing this results from those magnificent laws of co-existence, which form the basis of the science of comparative anatomy, and which give the highest interest to its discoveries.

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SECTION VIII.

PTERODACTYLE.^[56]

Among the most remarkable disclosures made by the researches of Geology, we may rank the flying reptiles, which have been ranged by Cuvier under the genus Pterodactyle; a genus presenting more singular combinations of form, than we find in any other creatures yet discovered amid the ruins of the ancient earth.^[57]

The structure of these animals is so exceedingly anomalous, that the first discovered Pterodactyle (Pl. 21) was considered by one naturalist to he a bird, by another as a species of bat, and by a third as a flying reptile.

This extraordinary discordance of opinion respecting a creature whose skeleton was almost entire, arose from the presence of characters apparently belonging to each of the three classes to which it was referred. The form of its head, and length of neck, resembling that of birds, its wings approaching to the proportion and form of those of bats, and the body and tail approximating to those of ordinary Mammalia. These characters, connected with a small skull, as is usual among reptiles, and a beak furnished with not less than sixty pointed teeth, presented a combination of apparent anomalies which it was reserved for the genius of Cuvier to reconcile. In his hands, this apparently monstrous production of the ancient world, has been convened into one of the most beautiful examples yet afforded by comparative anatomy, of the harmony that pervades all nature, in the adaptation of the same parts of the animal frame, to infinitely varied conditions of existence.

In the case of the Pterodactyle we have an extinct genus of the Order Saurians, in the class of Reptiles, (a class that now moves only on the land or in the water,) adapted by a peculiarity of structure to fly in the air. It will be interesting to see how the anterior extremity, which in the fore leg of the modern Lizard and Crocodiles is an organ of locomotion on land, became converted into a membraniferous wing; and how far the other parts of the body are modified so as to fit the entire animal machine for the functions of flight. The detail of this inquiry will afford such striking examples of numerical agreement in the component bones of every limb, with those in the corresponding limbs of living Lizards, and are at the same time so illustrative of contrivances for the adjustment of the same organ to effect different ends, that I shall select for examination a few points, from the long and beautiful analysis which Cuvier has given of the structure of this animal.

The Pterodactyles are ranked by Cuvier among the most extraordinary of all the extinct animals that have come under his consideration; and such as, if we saw them restored to life, would appear most strange, and most unlike to anything that exists in the present world.—"Ce sont incontestablement de tous les êtres dont ce livre nous révèle l'ancienne existence, les plus extraordinaire, et ceux qui, si on les voyait vivans, paroîtroient les plus étrangers à toute la nature actuelle." (Cuv. Oss. Foss. Vol. V. Pt. 11, p. 319.)

We are already acquainted with eight species of this genus, varying from the size of a Snipe to that of a Cormorant.^[58]

In external form, these animals somewhat resemble our modern Bats and Vampires: most of them had the nose elongated, like the snout of a Crocodile, and armed with conical teeth. Their eyes were of enormous size, apparently enabling them to fly by night. From their wings projected fingers, terminated by long hooks, like the curved claw on the thumb of the Bat. These must have formed a powerful paw, wherewith the animal was enabled to creep or climb, or suspend itself from trees.

It is probable also that the Pterodactyles had the power of swimming, which is so common in reptiles, and which is now possessed by the Pteropus Pselaphon, or Vampire Bat of the island of Bonin. (See Zool. Journ. No. 16, p. 458.) "Thus, like Milton's fiend, all qualified for all services and all elements, the creature was a fit companion for the kindred reptiles that swarmed in the seas, or crawled on the shores of a turbulent planet.

                                                                'The Fiend,
      O'er bog, or steep, through strait, rough, dense, or rare,
      With head, hands, wings, or feet, pursues his way,
      And swims, or sinks, or wades, or creeps, or flies,'
                                  Paradise Lost, Book II. line 947.

With flocks of such-like creatures flying in the air, and shoals of no less monstrous Ichthyosauri, and Plesiosauri swarming in the ocean, and gigantic Crocodiles, and Tortoises crawling on the shores of the primeval lakes and rivers, air, sea, and land must have been strangely tenanted in these early periods of our infant world."^[59]

As the most obvious feature of these fossil reptiles is the presence of organs of flight, it is natural to look for the peculiarities of the Bird or Bat, in the structure of their component bones. All attempts, however, to identify them with Birds are stopped at once by the fact of their having teeth in the beak, resembling those of reptiles: the form of a single bone, the os quadratum, enabled Cuvier to pronounce at once that the creature was a Lizard: but a Lizard possessing wings exists not in the present creation, and is to be found only among the Dragons of romance and heraldry;^[60] while a moment's comparison of the head and teeth with those of Bats (Pl. 21, and Pl. 22, M.) shows that the fossil animals in question cannot be referred to that family of flying Mammalia.

The vertebræ of the neck are much elongated, and are six or seven only in number, whereas they vary from nine to twenty-three in birds.^[61] In birds the vertebræ of the back also vary from seven to eleven, whilst in the Pterodactyles there are nearly twenty; the ribs of the Pterodactyles are thin and thread-shaped, like those of Lizards, those of birds are flat and broad, with a still broader recurrent apophysis, peculiar to them. In the foot of birds, the metatarsal bones are consolidated into one: in the Pterodactyles all the metatarsal bones are distinct; the bones of the pelvis also differ widely from those of a bird, and resemble those of a Lizard; all these points of agreement, with the type of Lizards, and of difference from the character of birds, leave no doubt as to the place in which the Pterodactyles must be ranged, among the Lizards, notwithstanding the approximation which the possession of wings seems to give them to Birds or Bats.

The number and proportions of the bones in the fingers and toes in the Pterodactyle, require to be examined in some detail, as they afford coincidences with the bones in the corresponding parts of Lizards, from which important conclusions may be derived.

As an insulated fact, it may seem to be of little moment, whether a living Lizard or a fossil Pterodactyle, might have four or five joints in its fourth finger, or its fourth toe; but those who have patience to examine the minutæ of this structure, will find in it an exemplification of the general principle, that things apparently minute and trifling in themselves, may acquire importance, when viewed in connexion with others, which, taken singly, appear equally insignificant. Minutiæ of this kind, viewed in their conjoint relations to the parts and proportions of other animals, may illustrate points of high importance in physiology, and thereby become connected with the still higher considerations of natural theology. If we examine the fore-foot of the existing Lizards, (Pl. 22, B.) we find the number of joints regularly increased by the addition of one, as we proceed from the first finger, or thumb, which has two joints, to the third, in which there are four; this is precisely the numerical arrangement which takes place in the three first fingers of the hand of the Pterodactyle; (Pl. 22, C. D. E. N. O. Figs. 30—38.) Thus far the three first fingers of the fossil reptile agree in structure with those of the forefoot of living Lizards; but as the hand of the Pterodactyle was to be converted into an organ of flight, the joints of the fourth, or fifth finger were lengthened, to become expansors of a membranous wing.^[62]

As the bones in the wing of the Pterodactyle thus agree in number and proportion with those in the fore foot of the Lizard, so do they differ entirely from the arrangement of the bones which form the expansors of the wing of the Bat.^[63]

The total number of toes in the Pterodactyles is usually four; the exterior, or little toe, being deficient; if we compare the number and proportion of the joints in these four toes with those of Lizards, (Pl. 22, F, G, H, I,) we find the agreement as to number, to be not less perfect than it is in the fingers; we have, in each case, two joints in the first, or great toe, three in the second, four in the third, and five in the fourth. As to proportion also, the penultimate joint is always the longest, and the ante penultimate, or last but two, the shortest; these relative proportions are also precisely the same, as in the feet of Lizards.^[64] The apparent use of this disposition of the shortest joints in the middle of the toes of Lizards, is to give greater power of flexion for bending round, and laying fast hold on twigs and branches of trees of various dimensions, or on inequalities of the surface of the ground or rocks, in the act of climbing, or running.^[65]

All these coincidences of number and proportion, can only have originated in a premeditated adaptation of each part to its peculiar office; they teach us to arrange an extinct animal under an existing family of reptiles; and when we find so many other peculiarities of this tribe in almost every bone of the skeleton of the Pterodactyle, with such modifications, and such only as were necessary to fit it for the purposes of flight, we perceive unity of design pervading every part, and adapting to motion in the air, organs which in other genera are calculated for progression on the ground, or in the water.

If we compare the foot of the Pterodactyle with that of the Bat, (see Pl. 22, K,) we shall find that the Bat, like most other mammalia, has three joints in every toe, excepting the first, which has only two: still these two, in the Bat, are equal in length to the three bones of the other toes, so that the five claws of its foot range in one strait line, forming altogether the compound hook, by which the animal suspends itself in caves, with its head downwards, during its long periods of hibernation; the weight of its body being, by this contrivance, equally divided between each of the ten toes. The unequal length of the toes of the Pterodactyle must have rendered it almost impossible for its claws to range uniformly in line, like those of the Bat, and as no single claw could have supported for a long time the weight of the whole body, we may infer that the Pterodactyles did not suspend themselves after the manner of the Bats. The size and form of the foot, and also of the leg and thigh, show that they had the power of standing firmly on the ground, where, with their wings folded, they possibly moved after the manner of birds; they could also perch on trees, and climb on rocks and cliffs, with their hind and fore feet conjointly, like Bats and Lizards.

With regard to their food, it has been conjectured by Cuvier, that they fed on insects, and from the magnitude of their eyes that they may also have been noctivagous. The presence of large fossil Libellulæ, or Dragon-flies, and many other insects, in the same lithographic quarries with the Pterodactyles at Solenhofen, and of the wings of coleopterous insects, mixed with bones of Pterodactyles, in the oolitic slate of Stonesfield, near Oxford, proves that large insects existed at the same time with them, and may have contributed to their supply of food. We know that many of the smaller Lizards of existing species are insectivorous; some are also carnivorous, and others omnivorous, but the head and teeth of two species of Pterodactyle, are so much larger and stronger than is necessary for the capture of insects, that the larger species of them may possibly have fed on fishes, darting upon them from the air after the manner of Sea Swallows and Solan Geese. The enormous size and strength of the head and teeth of the P. Crassirostris, would not only have enabled it to catch fish, but also to kill and devour the few small marsupial mammalia which then existed upon the land.

The entire range of ancient anatomy, affords few more striking examples of the uniformity of the laws, which connect the extinct animal of the fossil creation with existing organized beings, than those we have been examining in the case of the Pterodactyle. We find the details of parts which, from their minuteness should seem insignificant, acquiring great importance in such an investigation as we are now conducting; they show not less distinctly, than the colossal limbs of the most gigantic quadrupeds, a numerical coincidence, and a concurrence of proportions, which it seems impossible to refer to the effect of accident; and which point out unity of purpose, and deliberate design, in some intelligent First Cause, from which they were all derived. We have seen that whilst all the laws of existing organization in the order of Lizards, are rigidly maintained in the Pterodactyles; still, as Lizards modified to move like birds and Bats in the air, they received, in each part of their frame, a perfect adaptation to their state. We have dwelt more at length on the minutiæ of their mechanism, because they convey us back into ages so exceedingly remote, and show that even in those distant eras, the same care of a common Creator, which we witness in the mechanism of our own bodies, and those of the myriads of inferior creatures that move around us, was extended to the structure of creatures, that at first sight seem made up only of monstrosities.

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SECTION IX.

MEGALOSAURUS.^[66]

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 Monitor.

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.^[67] 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.^[68] 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 in weight, by being internally hollow, marrow, while their cylindrical form tended also to combine this lightness with strength.^[69]

The form of the teeth shows the 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.^[70]

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 mechanism will best be explained by reference to the figures in Pl. 23.^[71]

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 backwards, in the form of a pruning knife, (Pl. 23, Figs. 1. 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 likes 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 instruments of art.

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

SECTION X.

IGUANODON.^[72]

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 herbivore. 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 the remains of the Plesiosaurus, Megalosaurus, Hylæosaurus,^[73] and several species of Crocodiles and Tortoises in these deposites, 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.^[74] 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 doubt of the near connexion 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.^[75]

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 animals.^[76]

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 from 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.

Teeth.

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 away 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.

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 with 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.^[77]

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 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.^[78]

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 more efficient successor.^[79] 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 pieces 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 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.

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SECTION XI.

AMPHIBIOUS SAURIANS ALLIED TO CROCODILES.

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 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^[80] during the secondary periods, whilst the waters were abundantly stored with fishes, we might, à 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 mammalia abound.^[81]

During these grand periods of lacustrine mammalia, in which but few of the present genera of terrestrial carnivore had been called into existence, the important office of controlling the excessive increase of the aquatic herbivore 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 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 contemporaries.

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 freshwater 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.^[82] The living species of the Crocodile family are twelve in number, namely, one Giaval, eight true Crocodiles, and three Alligators. There are also many fossil species: no less than six of these have been made out by Cuvier, and several others, from the secondary and tertiary formations in England remain to be described.^[83]

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 unusually abundant store of these most essential organs.^[84] As Crocodiles increase to no less than four hundred times their original bulk, 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 Ichthyosauri and Plesiosauri, by any process of gradual transmutation or development. 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 termination of the secondary formations; when the Ichthyosauri and Plesiosauri, became extinct, and forms of Crocodiles, approaching to the Cayman and the Alligator, were for the first time introduced.

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SECTION XII.

FOSSIL TORTOISES, OR TESTUDINATA.

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 vertebrae, 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 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 co-extensively 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.^[85] 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 referable 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 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.^[86]

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 deposites; 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 in marine deposites, 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.^[87]

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 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.^[88]

It is not uncommon to find on the surface of sandstone, tracks which mark the passage of small Crustacea and other marine animals, whilst 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 ripple of agitated water upon sand.^[89]

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 deposite of earthy matter, before they were obliterated by any succeeding agitations of the water.

The nature of the impressions in Dumfriesshire 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.^[90]

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, would in no way interfere with the preservation of impressions made by feet, and speedily filled up by a succeeding deposite 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 animals 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.^[91]

The Historian or the Antiquary may have traversed the fields of ancient or of modern 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 passing 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.^[92]

SECTION IV.

FOSSIL FISHES.

The history of Fossil Fishes is the branch of Palæontology which has hitherto received least attention, in consequence of the imperfect 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 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.^[93]

The task of arranging all this disorder has 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.^[94] The results, of his inquiry 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.

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 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;^[95] the scales forming a kind of external skeleton, analogous to the crustaceous or 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 figures 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.^[96]

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 inquiry, and seem almost to add a new sense to our powers of geological perception. The general result is, that fossil Fishes approximate nearest to existing genera and species, in the most recent Tertiary deposites; 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.^[97]

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 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 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.^[98] 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.^[99]

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.^[100]

Sauroid Fishes in the Order Ganoid.

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 seventeen genera of Sauroid Fishes. Their only living representatives are the genus Lepidosteus,^[101] 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.^[102]

The teeth of the Sauroid Fishes are striated longitudinally towards the base, and have a hollow cone within. (See Pl. 27a, 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.^[103]

Pl. 27, Figs. ll, 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. 27a, Fig. 4, are fragments of jaws, containing many smaller teeth of the same kind. The external form of all these teeth are 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:^[104] their structure coincides entirely with that of the teeth of the living Lepidosteus osseus. (Pl. 27a, 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.^[105] In the Cretaceous formations they become extremely rare.^[106] They 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.^[107]

Fishes in Strata of the Carboniferous Order.

I select the genus Amblypterus (Pl. 27.,) 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 Saarbruck, in Lorraine;^[108] it is found also in Brazil. The character of the teeth in Amblypterus, and most of the genera of this early epoch, shows the habit of these Fishes to have been to feed on decayed sca-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 thebody, being not calculated for rapid progression, accords with this habit.

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 tin 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 show that they also fed on soft substances in similar situations.^[109]

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.^[110]

Fishes of the Magnesian Limestone, or Zechstein.

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, Spirifier, &c. shows 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.

Fishes of the Muschelkalk, Lias, and Oolite Formations.

The Fishes of the Muschelkalk are either peculiar to it, or similar to those of the Lias and Oolite. The figure engraved at Pl. 27c, 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.^[111] The use of this peculiar apparatus was to crush small shells, and small Crustacea, and to comminute putrescent seaweeds. The habits of the family of Pycnodonts appear to have been omnivorous, and their power of progression slow.^[112]

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. 54.) 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.^[113] One or two species only, having this peculiar armature of enamelled bony scales, 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.^[114]

Fishes of the Chalk Formation.

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 (Placoidean 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.

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.^[115]

Fishes of the Tertiary Formations.

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 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.^[116]

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 attributing them all to extinct genera.

The Fishes of Oeningen have, by all writers, been referred to a very recent local lacustrine deposite. 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 referable to one of the extinct genera of Monte Martre, but the greatest part are of existing genera. M. Agassiz considers the age of this formation as nearly coinciding with that of the Oeningen deposites.

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.

Family of Sharks.

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.^[117] 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. 27e, and 27f): 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. 27d. C. 3. a.) These were long considered to be jaws, and true teeth; more recently they have been ascertained to be dorsal spines of Fishes, and from their supposed defensive office, like those of the genus Balistes and Siluris, 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. 1. 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.^[118]

Fossil Spines, or Ichthyodorulites.^[119]

The bony spines of the dorsal fins of the Port Jackson Shark (Pl. 1. Fig. 18.) throw important light on the history of fossil Spines; and enable us to refer those very common, but little understood fossils, which have been called Ichthyodorulites, to extinct genera and species of the sub-family of Cestracionts. (See page 218.) Several living species of the great family of Sharks have 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 Ichthyodorulites: these hooks act as points of suspension and attachment, whereby the dorsal fin is connected with this bony spine, and its movements 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 movable 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.^[120]

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

Fossil Rays.

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. 27d, B. Fig. 14.) The genus Trygon, and Torpedo, occur also in the Tertiary formations.

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 shown 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 Cestruciont 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 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 sometimes 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 Developement and Transmutation of 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 organization 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.

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.

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1. The Author has recently been informed by Professor Kaup, of Darmstadt, that an entire head of this animal has been discovered at Epplesheim, measuring more than a yard in length and as much in breadth, and that he is preparing a description and figures of this head for immediate publication.
2. Linnean Transactions, Vol. XVII. Part 1.
3. The remains of the Megatherium have been found chiefly in the southern regions of America, and most abundantly in Paraguay; it appears also to have extended on the north of the equator as far as the United States. We have, for some time, possessed detailed descriptions of this animal by Cuvier, Oss. Foss. vol. 5, and a series of large engravings, by Pander and D'Alton, taken from a nearly perfect skeleton, sent in 1789 from Buenos Ayres to Madrid. Dr. Mitchell and Mr. Cooper have described, in the Annals of the Lyceum of Nat. Hist. of New York, May, 1824, some teeth and bones found in the marshes of the Isle of Skiddaway, on the coast of Georgia, which correspond with the skeleton at Madrid. Cuvier, Vol. V. part 2, p. 519.—In the year 1832, many parts of another skeleton were brought to England by Woodbine Parish, Esq. from the bed of the river Salado, near Buenos Ayres: these are placed in the museum of the Royal College of Surgeons in London, and will be described in the Trans. Geol. Soc. Lond. Vol. III. N. S. Part 3, by my friend Mr. Clift, a gentleman from whose great anatomical knowledge, I have derived most important aid, in my investigation of this animal.
4. The outside of the tooth, like that of an axe, is made of a comparatively sott material, viz. the crusta petrosa, (a a,) in closing a plate of enamel, (b b,) which is the hardest substance, or steel of the tooth. This enamel passes twice across the grinding surface, (z,) and forms the cutting edges of two parallel wedges, Y. b. b.: a longitudinal section of these wedges is seen, Pl. 6. v. w. x. y. Within the enamel, (b b,) is a central mass of ivory, (c,) which, like the external crust, (a) is softer than the enamel. A tooth, thus constructed of materials of unequal density, would have its softer parts, (a c,) worn down more readily than the harder plates of enamel, (b b.)

   We find a further nicety of mechanical contrivance, for producing and maintaining two transverse wedges upon the surface of each tooth, in the relative adjustment of the thickness, of the lateral and transverse portions of the plate of enamel, which is interposed between the external crust, (a,) and the central ivory, (c.) Had this enamel been of uniform thickness all round the central ivory, the tooth would have worn down equally to a horizontal surface. In the crown of the tooth, Pl. 6. Z. the plate of enamel is seen to be thin on the two sides of the tooth, whilst the transverse portions of the same plate, (b. b,) are comparatively thick and strong. Hence the weaker lateral portions of thin enamel wear away more rapidly, than the thicker and stronger transverse portions, (b b,) and do not prevent the excavation of the furrow across the surface of the Ivory, c.

5. The incisors of the Beaver, and other Rodentia, and tusks of the Hog and Hippopotamus, which require only an external cutting edge, and not a grinding surface, are constructed on the same principle as the cutting edge of a chisel or an adze; viz. a plate of hard enamel is applied to the outer surface only, of the ivory of these teeth, in the same manner as the outer cutting edge of the chisel and adze is faced with a plate of steel, welded against an inner plate of softer iron. A tooth thus constructed maintains its cutting edge of enamel continually sharp, by the act of working against the similarly constructed extremity of the tooth opposed to it.
6. Pl. 5, Fig. 11, represents the section of the cavity containing this pulp.
7. The tail of the Elephant is remarkably light and slender, with a tuft of coarse hair at its extremity, to brush off flies; that of the Hippopotamus is a few inches only in length, and Battened vertically, to act as a small rudder in swimming.
8. There is a similar expansion of the lower part of the Humerus in the Ant-eater, which employs its fore feet in digging up the solid hills of the Termite Ants.
9. At Pl. 5, beneath Fig. 1, are represented the fore-foot of an Armadillo (Daspyus Peba), and the fore-foot of the Chlamyphorus, each adapted, like that of the Megatherium, to form an instrument of peculiar power for the purpose of digging; and each presenting an extraordinary enlargement and elongation of the extreme bones of the toes, for the support of long and massive claws. At Pl. 5, Figs. 18, 19, the anterior parts of these animals are represented, and show how large a proportion the claws bear to the other parts of the body.
10. There is also a further peculiarity for the increase of strength in the manner in which that part, which, in most other animals, is an open space, called the ischiatic notch (Pl. 5, Fig. 2 c.) is nearly closed with solid bone by the union of the spines of the ischia with the elongated transverse processes of the sacral vertebrae, (a.)

    Further evidence of the enormous size and power in the muscles of the thigh and leg is afforded by the magnitude of the cavity in the sacrum, (Pl. 5. d,) for the passage of the spinal marrow: this cavity being about four inches in diameter, the spinal marrow must have been a foot in circumference. The extraordinary magnitude also of the nerves which proceeded from it to supply the leg, is indicated by the prodigious size of the sacral foramina.

11. It is probable that the large thick claw, Pl. 5 5', was placed on the second toe of the hind-foot. Its size approaches nearly to that of the first toe of this foot, and both of these differ materially in form and proportions, from the three more elongated and flatter claw-bones of the forefoot, the oblique form of which is peculiarly adapted for digging.
12. The resemblance between some parts of this fossil armour, and of the armour of an Armadillo, (Dasypus Peba) is extended even to the detail of the patterns of the tuberculated compartments into which they are divided, see Pl. 5, Figs. 12, 14. The increase of size in the entire shield is in both cases provided for, by causing the centre of every plate to form a centre of growth, around which the margin receives continual additions, as the increasing bulk of the body requires an increase in the dimensions of the bony case, by which it is invested. Figs. 15,1 16, 17, represent portions of the armour of the head, body, and tail piece of the Chlamyphorus. Figs. 18, 19, represent the manner in which the armour is disposed over the head and anterior part of the body of the Chlamyphorus, and Dasypus Peba. The body of the Megatherium, when covered with its corresponding coat of armour, must in some degree have resembled a tilted wagon.
13. In the Transactions of the Academy of Berlin, 1830, Professor Weiss has published an account of some bones of the Megatherium, discovered near Monte Video, accompanied by several fragments of bony armour. Much of this armour he refers without doubt to the Megatherium; other portions of it, and also many bones from the same district, he assigns to other animals. A similar admixture of bones and armour, derived from more than one species of animal, bearing a bony cuirass, is found in the collection made at several and distant points of the country above Buenos Ayres, by Mr. Parish. Although no armour was found with the fragments of the large skeleton, in the bed of the Salado, the rough broad flattened surface of a part of the crest of the ileum of this skeleton, (see Pl. 5, Fig. 2. r, s,) and the broad condition of the summit of the spinous processes of many vertebræ, and also of the superior convex portion of certain ribs on which the armour would rest, afford evidence of pressure, similar to that we find on the analogous parts of the skeleton of the Armadillo, from, which we might have inferred that the Megatherium also was covered with heavy armour, even had no such armour been discovered near bones of this animal in other parts of the same level district of Paraguay. In all these flattened bones the effects of pressure are confined to those parts of the skeleton, on which the armour would rest, and are such as occur in a remarkable degree in the Armadillo.
14. To animals that dig only occasionally, like Badgers, Foxes, and Rabbits, to form a habitation beneath the ground, but seek their food upon the surface, a defence of this kind would not only have been unnecessary but inconvenient.

    The Armadillo and Chlamyphorus are the only known animals that have a coat of armour composed of thick plates of bone, like that of the Megatherium, As this peculiar covering is confined to these quadrupeds, we can hardly imagine its use to be solely for protection against other beasts and insects; but as the Armadillo obtains its food by digging in the same dry and sandy plains, which were once inhabited by the Megatherium, and the Chlamyphorus lives almost entirely in burrows beneath the surface of the same sandy regions; they both probably receive from their cuirass the same protection to the upper parts of their bodies from sand and dust, which we suppose to have been afforded by its cuirass to the Megatherium. The Pangolins are covered with a different kind of armour, composed of horny movable scales, in which there is no bony matter.

15. The oldest strata in which any reptiles have yet been found are those connected with the magnesian-limestone formation. (Pl. 1, Sec. 16.) The existence of reptiles allied to the Monitor in the cupriferous slate and zechstein of Germany, has long been known. In 1834, two species of reptiles, allied to the Iguana and Monitor, were discovered in the dolomitic conglomerate, on Durdham Down, near Bristol.
16. The chief repository in which these animals have been found is the lias, at Lyme Regis; but they abound also along the whole extent of this formation throughout England, e. g. from the coast of Dorset, through Somerset and Leicestershire, to the coast of Yorkshire: they are found also in the lias of Germany and France. The range of the genus Ichthyosaurus seems to have begun with the Muschelkalk, and to have extended through the whole of the oolitic period into the cretaceous formation. The most recent stratum in which any remains of this genus have yet been found is the chalk marl at Dover, where they have been discovered by Mr. Mantell: I have found them in the gault, near Benson, Oxon.
17. Pl. 7, is a large and nearly perfect specimen of the Ichthyosaurus Platyodon, from the lias at Lyme Regis, being one of the splendid series of Saurians, Purchased in 1834 of Mr. Hawkins by the British Museum. Portions of the paddles, and many lost fragments, are restored from the corresponding parts which are preserved; a few vertebræ, and the extremity of the tail are also restored conjecturally. Beautiful and accurate lithographed figures of this specimen, and of the greater part of this collection, are published in Mr. Hawkins's Memoirs of Ichthyosauri and Plesiosauri, London, 1834. Pl. 8. Fig. 1, is a small specimen of the Ichthyosaurus Communis, from the lias at Lyme-Regis, belonging to the Geoll Soc. of London. Pl. 8, Fig. 2, a small Ichthyosaurus Intermedius, from the lias at Lyme Regis belonging to Sir Astley Cooper. Pl. 9, Fig. 1, an Ichthyosaurus Tenuirostris, from the lias of Street, near Glastonbury, in the collection of Rev. D. Williams. Fig. 2 is the continuation of the tail, and Fig. 3, the reverse of the head. The teeth in this species are small, and in due proportion to the slender character of the snout.
18. In the collection of Mr. Johnson at Bristol is a skull of Ichthyosaurus PIatyodon, in which the longer diameter of the orbital cavity measures fourteen inches.
19. In Pl. II, Fig. A, shows the manner in which the older tooth in the Crocodile becomes absorbed, by pressure of a younger tooth rising within the cavity of its hollow base. Fig. e, represents a transverse section of the left side of the lower jaw of an Ichthyosaurus, showing two teeth in their natural place, within the furrows of the jaw; the younger tooth, by lateral pressure, has caused absorption of the inside portion of the base of the older tooth. Fig, B, represents a transverse section of the entire snout of an Ichthyosaurus, in which the lower jaw exhibits on both sides, a small tooth (a,) which has caused partial absorption of the base of the larger tooth, (c.) In the upper jaw, the bases of two large teeth (d, d,) are seen in their respective furrows.
20. The bony sclerotic of the Ichthyosaurus approaches to the form of the bony circle in the eye of the Golden Eagle (Pl. 10, Fig. 5;) one of its uses in each case being to vary the sphere of distinct vision, in order to descry their prey at long or short distances. These bony plates also assist to maintain the prominent position of the front of the eye, which is so remarkable in birds. In Owls, whose nocturnal habits render distant vision impossible, Mr. Yarrel observes, that the bony circle (Pl. 10, Fig. 4,) is concave, and elongated forwards, so that the front of the eye is placed at the end of a long tube, and thus projects beyond the loose and downy feathers of the head; he adds; "The extent of vision enjoyed by the Falcons is probably denied to the Owls, but their more spherical lens and corresponding cornea give them an intensity better suited to the opacity of the medium in which they are required to exercise this power. They may be compared to a person near-sighted, who sees objects with superior magnitude and brilliancy when within the prescribed limits of his natural powers of vision, from the increased angle these objects subtend." Yarrel on the Anatomy of Birds of Prey, Zool. Journal, v. 3, p. 188.
21. There are analogous contrivances for the purpose of resisting pressure, and maintaining the form of the eye in fishes, by the partial or total ossification of the exterior capsule; but in fishes, this ossification is usually simple, though carried to a different extent in different species; and the bone is never divided transversely into many plates, as in Lizards and Birds; these capsules of the eye are often preserved in the heads of fossil ashes: they abound in the London clay; and occasionally occur in chalk.
22. These figures are selected from various plates by Mr. Conybeare and Mr. De la Beche. Fig. 1 is a restoration of the entire head of an Ichthyosaurus, in which each component bone is designated by the letters appropriated by Cuvier to the equivalent bones in the head of the Crocodile. In the lower jaw, u, marks the dental bone; v, the angular bone; x:, super angular or coronoid; y, articular bone; z, complementary; &, opercular. Fig. 2, is part of an under jaw of an Ichthyosaurus, showing the manner in which the flat bones, v, x, u, are applied to each other, towards the posterior part of the jaw. Figs. 3, 4, 5, 6, 7, show the manner in which these bones overlap, and lock into each other, at the transverse sections, indicated by the lines immediately above them in Fig. 2. Fig. 8, shows the composition of the bones in the lower jaw, as seen from beneath.
23. The coronoid bone, (x) is interposed between the dental, (u,) and opercular (&,) its fibres have a slanting direction, whilst those of the two latter bones are disposed horizontally; thus, the strength of the part is greatly increased by a regular diagonal bracing, without the least addition of weight or bulk; a similar structure may be noticed in the overlapping bones of the heads of fish, and in a less degree, in those of Turtles.—Geol. Trans. Lond. Vol. V. p. 565, and Vol. I. N. S. p. 112.
24. The sections of the vertebrae of a fish (A c. c.) present two hollow cones, united at their apex in the centre of each vertebræ, in the form of an hour-glass; but the bale of each cone, (b. b.) instead of terminating in abroad list surface, like the base of the hour-glass, is bounded by a thin edge, like the edge of a wine-glass, and by this alone touches the corresponding edge of the adjacent vertebrae. Between these hollow vertebræ, a soft and flexible intervertebral substance, in the form of a double solid cone (e. e.) is so placed that each hollow cone of bone plays on the cone of elastic substance contained within it, with a motion in every direction; thus forming a kind of universal joint, and giving to the entire column great strength, and power of rapid flexion in the water. But as the inflections in the perpendicular direction are less necessary than in the lateral, they are limited by the overlapping, or contiguity of the spines.

    This mode of articulation gives mechanical advantage to animals like fishes, whose chief organ of progressive motion is the tail; and the weight of whose bodies being always suspended in water, creates little or no pressure on the edges, by which alone the vertebra touch each other.

25. Sir E. Home has further remarked a peculiarity of the spinal canal, which exists in no other animals; the annular part (Pl. 12, D a. and E a.) being neither consolidated with the body of the vertebræ, as in quadrupeds; nor connected by a suture, as in Crocodiles; but remaining always distinct, and articulating' by a peculiar joint, resembling a compressed oval ball and socket joint, (D g. and E g.) And Mr. Conybeare adds, that this mode of articulation co-operates with the cup-shaped form of the intervertebral joints, in giving flexibility to the vertebral column, and assisting its vibratory motions; for, had these parts been consolidated, as in quadrupeds, their articulating processes must have locked the whole column together, so as to render such a motion of its parts impossible; but by means of this joint every part yields to that motion. The tubercle by which the transverse apophysis of the head of the rib articulates with the vertebræ, is seen at d.
26. The sterno-costal ribs probably formed part of a condensing apparatus, which gave these animals the power of compressing the air within its lungs, before they descended beneath the water. In the Lond. and Edin. Phil. Mag. Oct. 1833, Mr. Faraday has noticed a method of preparing the organs of respiration in man, so as considerably to extend the time of holding the breath in an impure atmosphere; or under water, as practised by pearl-fishers; and illustrated by experiments of Sir Graves C. Houghton. If a person inspires deeply, and ceasing with his lungs full of air, holds his breath as long as he is dale, the time during which he can remain without breathing will be double, or more than double, that which he could do if he held his breath without such deep inspiration. When Mr. Brunel, jun. and Mr. Gravatt descended in a diving-bell to examine the hole where the Thames had broken into the tunnel at Rotherhithe, at the depth of about thirty feet of water, Mr. Brunel, having inspired deeply the compressed air within the diving-bell, descended into the water below the bell; and found that he could remain twice as long under water, going into it from the diving-bell, at that depth, as he could under ordinary circumstances.

    Mr. Gravatt ha also informed me that he is able to dive, and remain three minutes under water, after inflating his lungs with the largest possible quantity of common air, by a succession of strong and rapid inspirations, and immediately compressing the lungs thus filled with air, by muscular exertion, and contraction of the chest, before he plunges into the water. By this compression of the lungs, the specific gravity of the body is also increased, and the descent is consequently much facilitated.

    All these advantages were probably united in the mode of respiration of the Ichthyosaurus, and also in the Plesiosaurus.

27. In this anomalous animal the Ornithorhynchus or Platypus, we have a quadruped clothed with fur, having a bill like a duck, with four webbed feet, suckling its young, and most probably ovoviviparous: the male is furnished with spurs.—See Mr. R. Owen's Papers on the Ornithorhynchus Paradoxus, in the Phil. Trans. London, 1832, Part II. and 1834, Part II. See also Mr. Owen's Paper on the same subject in Trans. Zool. Soc. Lond. Part III. 1835, in which he points out many approximations in the generative and other systems of this animal to the organization of reptiles.
28. In both these animals there is superadded to the ordinary type of bones in quadrupeds, an enlargement of the coracoid bone (c,) and a peculiar form of sternum, resembling the furcula of birds. In Pl. 12, Fig. 1, a. represents the peculiar sternum or furcula; b. b. the clavicles; c. c. the coracoid bones; d. d. the scapula; e. e. the humeri; f. g. the radius and ulna. At Fig. 2, the same letters are attached to the corresponding bones of the Ornithorhynchus.

    The united power of all these bones imparts to the chest and paddles peculiar strength for an unusual purpose; not so much to effect progressive motion (which, in the Ichthyosaurus, was produced with much greater facility and power by the tail,) as to ascend and descend vertically in quest of air and food.

29. The Echidna, or spiny Ant-eater, of New Holland, is the only known land quadruped that has a similar furcula and clavicles. As this animal feeds op Ants, and takes refuge in deep burrows, this structure may be subsidiary to its great power of digging. A cartilaginous rudiment of a furcula occurs also in the Dasypus; and seems subservient to the same purpose.
30. In the Ornithorhynchus, also, the membranous expansion, or web of the hind-feet, is very much less than that on the fore-foot.
31. The following description of these Coprolites, is given in my memoir on this subject, published in the Transactions of the Geological Society of London, 1829, (vol. iii. N. S. part i. p. 224, with three plates.)

    "In variety of size and external form, the Coprolites resemble oblong pebbles or kidney-potatoes. They, for the most part, vary from two to four inches in length, and from one to two inches in diameter. Some few are much larger, and bear a due proportion to the gigantic calibre of the largest Ichthyosauri; others are small, and bear a similar ratio to the more infantile individuals of the same species, and to small fishes: some are flat and amorphous, as if the substance had been voided in a semifluid state; others are Battened by pressure of the shale. Their usual colour is ash-gray, sometimes interspersed with black, and sometimes wholly black. Their substance is of a compact earthy texture, resembling indurated clay, and having a conchoidal and glossy fracture. The structure of the Coprolites at Lyme Regis is in most cases tortuous, but the number of coils is very unequal; the most common number is three: the greatest I have seen is six; these variations may depend on the various species of animals from which they are derived; I find analogous variations in the tortuous intestines of modern Skates, Sharks, and Dog-fish. Some Coprolites, especially the small ones, show no traces at all of contortion.

    The sections of these fœcal balls, (see Pl. 15, Figs. 4, and 6,) show their interior to be arranged in a folded plate, wrapped spirally round from the centre outwards, like the whorls of a turbinated shell; their exterior also retains the corrugations and minute impressions, which, in their plastic state, they may have received from the intestines of the living animals. (See Pl. 15, Figs. 3, and 10 to 14.) Dispersed irregularly and abundantly throughout these petrified fœces, are the scales, and occasionally the teeth and bones of fishes, that seem to have passed undigested through the bodies of the Saurians; just as the enamel of teeth and sometimes fragments of bone, are found undigested both in the recent and fossil album græcum of hyænas. These scales are the hard bright scales of the Dapedimn politum, and other fishes which abound in the lias, and which thus appear to have formed no small portion of the food of the Saurians. The bones are chiefly vertebrae of fishes and of small Ichthyosauri; the latter are less frequent than the bones of fishes, but still are sufficienly numerous, to show that these monsters of the ancient deep, like many of their successors in our modern oceans, may have devoured the small and weaker individuals of their own species."

32. Professor Jæger has recently discovered many Coprolites in the alum slate of Gaildorf in Wirtemberg; a formation which he considers to be in the lower region of that part of the new red sandstone formation which in Germany is called Keuper; and which contains the remains of two species of Saurians.

    In the United States Dr. Dekay has also discovered Coprolites in the Green-sand formation of Monmouth, in New Jersey, see Pl. 15, Pig. 13.

33. This specimen has been presented by Viscount Cole to the Geological Collection of the University of Oxford. It affords decisive proof that the substances in question cannot be referred to adventitious matter, placed accidentally in contact with the fossil body, inasmuch as the large coprolitic mass is enclosed between the back bone and the right and left series of ribs, of which the greater number remain nearly in their natural position. The quantity of this coprolite is prodigious, when compared with the size of the animal in which it occurs; and if we were not acquainted with the powers of the digestive organs of reptiles and fishes and their capacity of gorging the larger animals that form their prey; the great space within these fossil skeletons of Ichthyosauri, which is occasionally filled with coprolitic matter, would appear inexplicable.
34. According to Professor Agassiz, the scales of Pholidophorus limbatus, a species very frequent among the fossils of the lias, are more abundant than those of any other fish in the Coprolites found in that formation at Lyme Regis; and show that this species was the principal food of these reptiles. In Coprolites from the coal formation, near Edinburgh, he has also recognised the scales of Palæniscus, and of other fishes that are often found entire in strata that accompany the coal of that neighbourhood. Scales of the Zeus Lewisiensis, a fish discovered by Mr. Mantell, in the chalk, occur in Coprolites derived from voracious fishes during the deposition of this formation.
    
    A Coprolite from the lias, (Pl. 15, Fig. 3,) remarkable for its spiral convolutions, and vascular impressions, affords a striking example of the minute accuracy with which investigations are now conducted by naturalists, and of the kind of evidence which comparative anatomy contributes in aid of, geological inquiry. On one side of this Coprolite, there is a small scale, (Fig. 3, a,) which I could only refer to some unknown fish, of the numerous species that occur in the lias. The instant I showed it to M. Agassiz, he not only pronounced its species to be the Pholidophorus limbatus; but at once declared the precise place which this scale had occupied upon the body of the fish. A minute, tube upon its inner surface, (Pl. 15, Fig, 3',) scarcely visible without a microscope, showed it to have been one of those which form the lateral line of perforated scales. that pass from the head towards the tail, one on each side of every fish; and convey a tube for the transmission of lubricating mucus from glands in the head, to the extremity of the body. The place of the scale in this line, had been on the left side, not far from the the head. Fig. 3″, is the upper surface of a similar scale, showing at e the termination of the mucous duct.
35. These cone-shaped bodies are made up of a flat and continuous plate of digested bone, coiled round itself whilst it was yet in a plastic state. The form is nearly that which would be assumed by a piece of riband, forced continually forward into a cylindrical tube, through a long aperture in its side. In this case, the riband moving onwards, would form a succession of involuted cones, coiling one round the other, and after a certain number of turns within the cylinder, (the apex moving continually downwards,) these cones would emerge from the end of the tube in a form resembling that of the Coprolites, Pl. 15, Figs. 3, 5, 7, 10, 11, 12, 13, 14. In the same manner, a lamina of coprolitic matter would be coiled up spirally into a series of successive cones, in the act of passing from a small spiral vessel into the adjacent large intestine. Coprolites thus formed fell into, soft mud, whilst it was accumulating at the bottom of the sea, and together with this mud, (which has subsequently been indurated into shale and stone,) they have undergone so complete a process of petrifaction, that in hardness, and beauty of the polish of which they are susceptible, they rival the qualities of ornamental marble.

    Fig. 6, shows a longitudinal section through the axis of a coprolite, from the inferior chalk, in which this involute conical form is well defined. Fig. 4, is the transverse section of another Coprolite from the lias, showing the manner in which the plate coils round itself, till it terminates externally in a broken edge, (at b.) In all the figures the letter b, marks the transverse section of this plate, where it is broken off near the termination of its outer coil; the sections at b, show also the size and form of the flattened passage through the interior of the screw.

    A lamina of tenacious plastic substance pressed continually forwards from the interior of such a screw, into the cavity of the large intestine, would coil up spirally within it, until it attained the largest size admitted by its diameter; from this coil successive portions would be broken off abruptly, (at b,) and descending into the cloaca would be thence discharged into the sea.

36. These impressions cannot have been derived from the membrane of the inferior large intestine, because they are continued along those surfaces of the inner coils of the Coprolite, which became permanently covered by its outer coils, in the act of passing from the spiral tube into this large intestine.
37. Paley, in his chapter on mechanical compensations in the structure of animals, mentions contrivance similar to that which we attribute to the Ichthyosaurus, as existing in a species of Shark, (the Alopecias, Squalus Vulpes, or Sea Fox.) "In this animal, he says, the intestine is straight from one end to the other: but, in this straight, and consequently short intestine, is a winding, cork-screw, spiral passage, through which the food, not without several circumvolutions, and in fact by a long route, is conducted to its exit. Here the shortness of the gut is compensated by the obliquity of the perforation."

    Dr. Fitton has called my attention to a passage in Lord King's Life of Locke, 4°. p. 166, 167, from which it, appears that the importance of a spiral disposition within the intestinal canal, which he observed in many preparations in the collection of anatomy at Leyden, was duly appreciated by that profound philosopher.

38. See Mantell's Geol. of Sussex, Pl. 38. I learn from Mr. Mantell, that the form of the Coprolites within the Macropoma most nearly resemble those engraved, Pl. 15, Figs. 8, 9, of the present work: he also conjectures that the more tortuous kinds, (Pl. 15, Figs. 5, 7,) long known by the name of Juli, and supposed to be fossil fir cones, may have been derived from fishes of the Shark family, (Ptychodus) whose large palatal teeth (Pl. 27. f) abound in the same localities of the chalk formation with them, at Steyning and Hamsey.
39. As these Cololites are most frequently found insulated in the lithographic limestone, M. Agassiz has ingeniously explained this fact by observing the process of decomposition of dead fishes in the lakes of Switzerland. The dead fish floats on the surface with its belly upwards, until the abdomen is so distended with putrid gas, that it bursts: through the aperture thus formed the bowels come forth into the water, still adhering together in their natural state of convolution. This intestinal mass is soon torn from the body by the movement of the waves; the fish then sinks, and the bowels continue a long time floating on the water: if cast on shore, they remain many days upon the sand before they are completely decomposed. The small bowels only are thus detached from the body, the stomach and other viscera remain within it.

    We owe this illustration of the nature of these fossil bodies, whose hitherto been inexplicable, to the author of a most important work on fossil fishes, now under publication at Neuchatel. His qualifications for so great and difficult a task are abundantly guarantied by the fact, that Cuvier, on seeing the progress he had made, at once placed at the disposal of Professor Agassiz the materials he had himself collected towards a similar work.

40. Le temps qui répand de la dignité sur tout ce qui échappe à son pouvoir destructeur, fait voir ici un exemple singulier de son influence: ces substances si viles dans leur origine, etant rendues a la lumiére après tant de siécles, deviennent d'une grande importance puis qu'elles servent a remplir un nouveau chapitre dans l'histoire naturelle du globe.—Bulletin Soc. Imp. de Moscow, No. VI. 1833, p. 23.
41. See Pl. 16, 17, 18, 19.
42. Cet habitant de l'ancien monde est peut-être la plus hétéroclite et celui de tous qui paroit le plus mériter le nom de monstre.—Oss. Foss. V. Pt. 2, p. 476.
43. The first specimens of this animal were discovered in the lias of Lyme Regis, about the year 1823, and formed the foundation of that admirable paper (Geol. Trans. Lond. vol. 5, Pt. 2.) in which Mr. Conybeare and M. De la Beche established and named this genus. Other examples have since been recognised in the same formations in different parts of England, Ireland, France, and Germany, and in formation of various ages, from the muschel kalk upwards to the chalk. The first specimen discovered in a state approaching to perfection, was that in the collection of the Duke of Buckingham, (figured in the Geol. Trans. Lond. N. S. Vol. 1, Pt. 2, Pl. 48.) Another specimen, nearly entire, in the collection of the British Museum, eleven feet in length, is figured in our second volume, (Pl. 16;) and at Pi. 17, a still more perfect fossil skeleton, also in the British Museum, discovered by Mr. Hawkins, in the lias at Street, near Glastonbury. At Pl. 16 is also copied Mr. Conybeare's restoration of this animal, from dislocated fragments, before any entire skeletons were found. The near approach of this restoration to the character of the perfect skeletons, affords a striking example of the sure grounds on which comparative anatomy enables us to reconstruct the bodies of fossil animals, from a careful combination of insulated parts. The soundness of the reasoning of' Cuvier, on the fossil quadrupeds of Montmartre, was established by the subsequent discovery of skeletons, such as he had conjecturally restored from insulated bones. Mr. Conybeare's restoration of the Plesiosaurus Dolichodeirus, (Pl. 16,) was not less fully confirmed by the specimens above-mentioned.
44. See Pl. 16, 17, 18.
45. Mr. Conybeare, in the Geol. Trans. second series, vol. 1, part 1, Pl. 19, has published figures of the superior and lateral view of a nearly perfect head of this animal. Our figure, Pl. 18, Fig. 2, represents the head of the specimen in the British Museum, of which the entire figure, on a smaller scale, is given in Pl. 16. The head is in a supine position; the upper jaw is distorted, and shows several of the separate alveoli that contained the teeth, and also the posterior portion of the palate. The under jaw is but little disturbed.

    A figure of another lower jaw is given at Pl. 18, Fig. 1, taken from a specimen also in the British Museum, found by Mr. Hawkins, at Street.

    Pl. 19, Fig. 3, represents the extremity of the dental bone of another lower jaw, in the same collection, retaining several teeth in the anterior sockets, and also exhibiting a series of new teeth, rising within an anterior range of small cavities. This arrangement for the formation of new teeth, in cells within the bony mass that contains the older teeth, from which they shoot irregularly forwards through the substance of the bone, forms an important point of resemblance whereby the Plesiosaurus assumes, in the renovation of its teeth, the character of Lizards, combined with the position of the perfect teeth in distinct alveoli, after the manner of Crocodiles.

    The number of teeth in the lower jaw was fifty-four, which, if met by a corresponding series in the upper jaw, must have made the total number to exceed one hundred. The anterior part of the extremity of the jaw enlarges itself like the bowl of a spoon, to allow space for the reception of the six first teeth on each side, which are the largest of all.

46. To compensate for the weakness that would have attended this great elongation of the neck, the Plesiosaurus had an addition of a series of hatchet-haped processes, on each side of the lower part of the cervical vertebrae. (Pl. 17, and Pl. 19, 1, 2.) Rudiments and modifications of these processes exist in birds, and in long-necked quadrupeds. In the Crocodiles they assume a form, most nearly approaching that which they bear in the Plesiosaurus.

    The bodies of the vertebræ also more nearly resemble those of certain fossil Crocodiles, than of Ichthyosauri or Lizards; they agree further with the Crocodile, in having the annular part attached to the body by sutures; so that we have in the neck of the P. Dolichodeirus a principle of construction resembling that of the vertebrae of Crocodiles; combined with an elongation very much exceeding that of the longest neck in birds, and such as occurs in no other known animal of the extinct or living creations. The length of the neck in P. Dolichodeirus is nearly five times that of the head; that of the trunk four times the length of the head, and of the tail three times; the head itself being one-thirteenth part of the whole body.—See Geol. Trans. Lond. Vol. 5, p. 559, and Vol. I. N. S. p. 103, et seq.

47. See Pl. 16, 17, 18.
48. The ventral portion of each rib, (Pl. 17, and Pl. 18, 3, b,) appears to have been composed of three slender bones fitted to one another by oblique grooves, allowing of great expansive movement during the inflation of the lungs: the manner in which these triple bones were folded over one another, is best seen in a single series between a, and b, the upper ends of the ventral portions of the ribs (b) have been separated by pressure, from the lower ends of the vertebral portions. (d.)
49. We have no means to verify this ingenious conjecture, that the Plesiosaurus may have been a kind of sub-marine Chameleon, possessing the power of altering the colour of its skin; it must however be admitted that such a power would have been of much advantage to this animal, in defending it by concealment from its most formidable enemy the Ichthyosaurus, with which, its diminutive head and long slender neck, must have rendered it a very unequal combatant, and from whose attacks its slow locomotive powers must have made escape by flight impossible; the enlarged condition of the lungs, would also have been of great advantage in diminishing the frequency of its ascents to the surface, to inspire air; an operation that must have been attended with constant danger, in a sea, thickly swarming with Ichthyosauri. Dr. Stark has recently observed that certain fishes, especially minnows, have a tendency to assume the colour of the vessel in which they are kept. (Proceedings Zool. Soc. Lond. July, 1833.) As in animals of this class there are no lungs, this change of colour must arise from other causes than that to which it has been attributed in the Chameleon.
50. See Pl. 16, 17, 19.
51. The number of joints representing the phalanges of the fingers and toes exceeds that in the Lizards and Birds, and also in all Mammalia, excepting the Whales, some of which present a similar increase of number to accommodate them to the corresponding office of a paddle. The mode of connexion between the joints was (like that in the Whales,) by synchondrosis. The phalanges of the Plesiosaurus present a link, between the still more numerous and angular joints of the paddle of the Ichthyosaurus, and the phalanges of land quadrupeds, which are more or less cylindrical; in these sea Lizards they were flattened, for the purpose of giving breadth to the extremities as organs of swimming. As its paddles give no indication of having carried even such imperfect claws, as those of the Turtle and Seals, the Plesiosaurus apparently could have made little or no progress in any other element than water.
52. The Monitors form a genus of Lizards, frequenting marshes and the banks of rivers in hot climates; they have received this name from the prevailing, but absurd, notion that they give warning by a whistling noise, of the approach of Crocodiles and Caymans. One species, the Lacerta nilotica, which devours the eggs of Crocodiles, has been sculptured on the monuments of ancient Egypt.
53. Remains of the Mosasaurus have been discovered by Mr. Mantell in the upper chalk near Lewes, and by Dr. Morton in the green sand of Virginia.
54. The Grampus is from 20 to 25 feet long, and very ferocious, feeding on seals and porpoises as well as on fishes.
55. The teeth have no true roots and are not hollow, as in the Crocodiles, but when full grown, are entirely solid, and united to the sockets by a broad and firm base of bone, formed from the ossification of the pulpy matter which had secreted the tooth, and still further attached to the jaw by the ossification of the capsule that had furnished the enamel. This indurated capsule, passed like a circular buttress around its base, tending to make the tooth an instrument of prodigious strength. The young tooth first appeared in a separate cell in the bone of the jaw, (Pl. 20, h.) and moved irregularly across its substance, until it pressed against the base of the old tooth; causing it gradually to become detached, together with its base by a kind of necrosis, and to fall off like the horns of a Deer. The teeth, in the roof of the mouth, are also constructed on the same principle with those in the jaw, and renewed in like manner.
56. See Pl. 1, Figs. 42, 43, and Plates 21, 22.
57. Pterodactyles have hitherto been found chiefly in the quarries of lithographic limestone of the jura formation at Aichstadt and Solenhofen; a stone abounding in marine remains, and also containing Libellulæ, and other insects. They have also been discovered in the lias of Lyme Regis, and in the oolitic slate of Stonesfield.
58. In Pl. 21, I have given an engraving of the Pterodactylus longirostris, which was first published by Collini, and formed the basil on which this genus was established

    At Pl. 22, O. is engraved the smallest known species, P. Breviostris, from Solenhofen, described by Professor Soemmering.

    A figure and description of a third species, P. macronyx, from the lias at Lyme Regis, have been published by myself; (Geol. Trans. Lond. second series, Vol. 3, Pt. 1.) This species was about the size of a Raven, and its wings, when expanded, must have been about four feet from tip to tip. A fourth species, P. crassirostris, has been described by Professor Goldfuss. In Pl. 22, N. I have given a reduced copy of his plate of the specimen; and in Pl. 22, A. a copy of his restoration of the entire animal. Count Munster has described another species, P. medius. Cuvier describes some bones of a species, P. grandis, four times as large as P. longirostris, which latter was about the size of a Woodcock. Professor Goldfuss has described a seventh species from Solenhofen, P. Munsteri; and has proposed the name P. Bucklandi, for the eighth undescribed species found at Stonesfield.

59. Geol. Trans. Lond. N. S. Vol. III. part. 1.
60. One diminutive living species of Lizard, (the Draco volans, see Pl. 22, L.) differs from all other Saurians, in having an appearance of imperfect wings, produced by a membranous expansion of the skin over the false ribs which project almost horizontally from the back; the membrane expanded by these false ribs, acts like a parachute to support the animal in leaping from tree to tree, but has no power to beat the air, or become an instrument of true flight, like the arm or wing of Birds and Bats; the arm or fore leg of the Draco volans differs not from that of common Lizards.
61. In one species of Pterodactyle, viz. the P. macronyx, Geol. Trans. N. s. V. iii. pl. 27, page 220, from the lias at Lyme Regis, there is an unusual provision for giving support and movement to a large head at the extremity of a long neck, by the occurrence of bony tendons running parallel to the cervical vertebræ, like the tendons that pass along the back of the Pigmy Musk (Moschus pigmæus,) and of many birds. This provision does not occur in any modern Lizards, whose necks are short, and require no such aid to support the head. In the compensation which these tendons afforded for the weakness arising from the elongation of the neck, we have an example of the same mechanism in an extinct order of the most antient reptiles, which is still applied to strengthen other parts of the vertebral column, in a few existing species of mammalia and birds.
62. Thus in the P. Longirostris (Pl. 21, 39—42.) and P. Brevirostris, (Pl. 22, Fig. O, 39—42,) the fourth finger is stated by Cuvier to have four elongated joints, and the fifth or ungual joint to be omitted, as its presence is unnecessary. In the P. Crassirostris, according to Goldfuss (Pl. 22, Figs. A, N,) this claw is present upon the fourth finger, (43) which thus has live bones, and the fifth finger is elongated to carry the wing. Throughout all these arrangements in the fore-foot, the normal numbers of the type of Lizards are maintained.

    If, as appears from the specimen engraved by Goldfuss, of P. Crassi rostris, (Pl. 22, N, 44, 45,) the fifth finger was elongated to expand the wing, we should infer from the normal number of joints in the fifth finger of Lizards being only three, that this wing finger had but three joints. In the fossil itself the two first joints only are preserved, so that his conjectural addition of a fourth joint to the fifth finger, in the restored figure, (Pl. 22, A, 47,) seems inconsistent with the analogies, that pervade the structure of this, and of every other species of Pterodactyle, as described by Cuvier.

63. The Bat, see Pl. 22, M, 30, 31, the first finger or thumb alone, is free, and applied to the purpose of suspension and creeping; the expansors of the wing are formed by the metacarpal bones, (26—29,) much elongated and terminated by the minute phalanges of the other four fingers, 32—45, thus presenting an adaptation of the hand of the mammalia to the purposes of flight, analogous to that which in the fossil world, the Pterodactyle affords with respect to the hand of Lizards.
64. According to Goldfuss the P. Crassirostris had one more toe than Cuvier assigns to the other species of Pterodactyles; in this respect it is so far from violating the analogies we are considering, that it adds another approximation to the character of the living Lizards; we have seen that it also differs from the other Pterodactyles, in having the fifth, instead of the fourth finger elongated, to become the expansor of the wing.

    It is however probable that the fifth toe had only three joints, for the same reasons that are assigned respecting the number of joints in the fifth finger. In the P. Longirostris, Cuvier considers the small bone, (Pl. 21, 5, 6,) to be a rudimentary form of the fifth toe.

65. A similar numerical disposition prevails also in the toes of birds, attended by similar advantages.
66. 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 and having their cavities filled with the light, material of 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.
67. See Geol. Trans. 2d series, Vol; 3, p. 427, Pl. 41.
68. I learn from Mr. Owen that the long bones of land Tortoises have a close cancellous internal structure, but not a medullary cavity.
69. The medullary cavities in the fossil bones of the Megalosaurus, from Stonesfield, are usually filled with calcareous spar. In the Oxford Museum there is a specimen from the Wealden freshwater 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 is 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 connexion 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.

70. 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.
71. 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 the 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.
72. See Pl. 1, Fig. 45, and Pl. 24; and Mantell's Geology of Sussex, and of the Southeast of England.
73. The Hylæosaurus, or Lizard of the Weald, was discovered in Tilgate Forest, in Sussex, in 1832. This extraordinary Lizard was probably about twenty dive 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.
74. 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 deposites 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, shows 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 freshwater deposites 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.
75. 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 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.

76. From a careful comparison of the 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 proportionate measure of the following parts of this extraordinary reptile:

    	Feet.
    Length from snout to the extremity of the tail	70
    Length of tail	52½
    Circumference of body	14½

    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 vertebra: is much less in proportion than in the Iguana, and shows the entire tail to have been comparatively shorter.

77. 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.
78. 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 the crown was thus perpetually 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. 2. 6. 8. 9. 12.) As these saws were gradually worn away, the cutting power was transferred to the enamel in front, 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 googes, 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.)

79. 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.
80. 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.
81. One of these, found by Mr. Spencer in the London clay of the Isle of Sheppy, is engraved, Pl. 25', Fig. 1. Crocodiles of this kind have been fund in the chalk of Meudon, in the plastic clay of Auteuil, in the London day, 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 no 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.

82. 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.
83. 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.

84. This mode of dentition has been already exemplified in speaking of the dentition of the Ichthyosaurus, P. 136, and Pl. 11. A.
85. 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.
86. Plate 25', Fig. 4, represents a Turtle from the slate of Glaris: it is shown 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 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 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 referable 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".
87. 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 deposites 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 Testudinsts, occur in the Oolite slate of Stonesfield, near Oxford.
88. See Dr. Duncan's account of tracks and footmarks of animals, impressed on sandstone in the quarry of Corn Cockle Muir, Dumfriesshire 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.

89. In 1831, Mr. G. P. Scrope, after visiting the quarries of Dumfries, 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. Mag. 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 extremity 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 shows the very quiet condition of the bottom, and the gentle action of the water, which brought the materials that covered them over, without disturbing 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 alteration of intervals of repose with periods of violence, during the destructive processes by which derivative strata were formed.

90. On comparing some of these impressions with the tracks which, 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 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.

91. 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.
92. A similar discovery of fossil footsteps has recently been made in Saxony, at the village of Hessberg, near Hildburghausen, in several quarries of gray quartzose sandstone, alternating 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 footsteps follow one mother 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 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 64, 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 footsteps, correspond most accurately. The hind foot (Pl. 26″,) is drawn from one on this slab. Pl. 26‴ is drawn from a plastercast in the British Museum, taken from another slabs 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 deposite 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.

93. The most celebrated deposites of fossil Fishes in Europe are the coal formation of Saarbruck, 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 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.

94. 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 extinct.—Agassiz
95. 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 relations 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, climate and occupation upon the land. The scales of Fishes show a similar adaptation to their varied place and occupation 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.

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

    First Order, PLACOIDIANS (Pl. 27, Figs. 1, 2, Etym. πλαξ, 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. γανος, 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. 27a, Fig. 1;) 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. κτενα, 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. 21, Figs. 7, s. Etym. κυκλος, 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.

97. 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 deposites 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.
98. M. Agassiz observes that fossil Fishes in the same formation present greater variation 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.
99. 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.
100. Thus the slate of Engi, in the canton of Glaris, in Switzerland, 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 Planer kalk; hence he infers that the Glaris slate is an altered condition of an argillaceous deposite, 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 referable to genera that characterize the strata of the Oolitic series, the Wealden deposites 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 commencement 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 deposites of Oeningen, and, of Aix in Provence, with that of the Molasse of Switzerland.

101. Lepidosteus Agassiz—Lepisosteus Lacépéde.
102. 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.
103. 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.
104. 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 deposite was formed in a freshwater lake, or estuary. It has been recognised 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, 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. 27a, 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.

105. The Aspidorhynchus, from the Jurassic limestone of Solenhofen, (Pl. 27a, Fig. 5,) represents the general character of the Sauroid Fishes.
106. The Macropoma is the only genus of Sauroid Fishes yet found in the Chalk of England.
107. 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.
108. The Fishes at Saarbruek 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.
109. 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.
110. 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 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 vertebra. 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 Palæoniseus and Polypterus.

111. Pl. 27c. 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.
112. A similar apparatus occurs in a living family of the Order Cycloids, in the case of the modern omnivorous Sea Wolf; 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.
113. 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 off armour. The use of such a 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 deposites, may have been to defend their bodies against waters 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 membranous and horny scales of most modern Fishes.
114. The most remarkable of these are the genus Lepidotus, Pholidophorus, Pycnodus, and Hybodus.
115. It has been already stated, that the remarkable deposite 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 (Planer 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.

116. 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.
117. M. Agassiz has ascertained the existence of more than one hundred and fifty extinct species of fossil Fishes allied to this family.
118. 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 tessellated pavement. (Pl. 27d. A. 1, 3, 4, and Pl. 27d, 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 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 27e, Figs. 1, 2, represent a series of teeth of the genus Acrodus, in the family of Cestracionts, from the lias of Somersetshire; and Pl. 27f, a series of teeth of the genus Ptychodus, in the same family, a genus 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. 27d, A.) is the only living species in the family of Sharks that has flat tessellated teeth, and enables us to refer numerous fossil teeth of similar construction to the same family. As the small anterior cutting teeth (Pl. 27d, 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 are distinguished from those of true Sharks by being plicated, both on the external and internal surface of the enamel. (See Plate 27d. B. Figs. 8, 9, 10.) Plate 27d C. 1re. 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 and in the Wealden formation.

     Another genus in the sub-family of Hybodonts, is the Onchus, found in the Liss at Lyme Regis; the teeth of this genus are represented, Pl. 27d. 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 deposites to the present era.. (Pl. 27d. 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 Crustacea, 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 characterize the teeth of living Sharks. Not one species of the blunt-toothed Cestraciont family has yet been discovered in any Tertiary formation.

119. See Pl. 27d. C. 3.
120. 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 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.