Chelys fimbriata, the "Matamata," the only species of this genus, inhabits the rivers of Guiana and Northern Brazil. Besides the nuchal, there are seven neural plates; the last pair of costals form a median suture. Nasal bones are absent. The jaws are very weak. The Matamata has a very peculiar appearance. The nose is produced into a long, soft tube, at the end of which open the tiny nostrils. The eyes are very small, and the orbits are placed very near the anterior end of the skull, while the parietal region is broad and much elongated (Fig. 87, p. 400). The quadrates are drawn out into trumpet-shaped tubes. The hyoid apparatus is very large, with enormous anterior and posterior horns. The head and neck are as long as or even longer than the carapace, which is covered with thick, lumpy shields. The skin of the thick neck, of the sides and under parts of the head, is produced into many soft arborescent excrescences or fimbriae, those of the chin and throat and the large ear-flaps being movable at will, and probably used to attract fishes and other prey. The tail is very short. The fore- and hind-limbs are webbed, the former with five, the latter with four claws. Old specimens, which reach a total length of three feet, are uniformly dark brown, and look like a log covered with rough bark. The young are far less ugly, with black and yellow spots on the shell, and with dark stripes along the neck.

Very little is known about the habits of this peculiar creature. It is said to lie submerged in the water, waiting for fishes, frogs, or tadpoles, which are attracted by the playing motions of its cutaneous excrescences. The jaws being so weak, and being covered with a partly soft lip-like skin, it is probable that they are not used for seizing the prey, but that the latter is engulfed into the mouth with the inrush of water into the throat. That this can be widened enormously is indicated by the greatly developed hyoid apparatus.

Chelodina.–The neck is long and slender, the head small and smooth. The nuchal is terminal; the intergular is large. The neural plates are completely suppressed, all the eight pairs of costal plates meeting in the middle line. The shell is very flat. Anterior and posterior limbs entirely webbed, and with only four claws. The tail is very short. Three species in Australia, one in New Guinea.

Ch. longicollis reaches a shell-length of ten inches. It inhabits Southern Australia. The illustrations make a detailed description unnecessary. The colour of the dorsal shield is uniformly dark rich brown, while the shields of the under surface are yellow, with broad dark brown lines along the sutures. These "long-necked Chelodines" have a striking appearance, when they swim or creep about, with the neck either stretched out straight or bent horizontally in an S-shape. The whole creature looks neat and elegant; the iris is pale yellow, and gives the eye a very intelligent expression. They keep well in captivity, provided they are given the choice of land and water. My own prefer to spend most of the day on land, preferably under the ledge of a stone, or perched upon the stone itself if the latter is in the shade, and not too much exposed to view. There they lie motionless, with the neck neatly tucked under the shell, either to the right or to the left. Although the eyelids may be closed, they can see well enough, owing to the transparent condition of the lower lid. They feed in the water upon soft animals, as for instance worms, smooth caterpillars, cockroaches or little frogs; and they also take meat readily, provided this is moved about. The food is invariably taken with a quick sideward jerk of the neck and head.

My specimens soon became so tame that they left the water, and ran up to me with the necks stretched to their full length, then snatching the bit of food, and retiring into the pond to swallow it. When left to themselves they are rather nocturnal in their feeding habits. Now and then they tuck themselves away for weeks without feeding, for instance when they go through a regular term of aestivation in the summer. The last winter they spent buried in the moss, but occasionally, especially on bright and sunny days, they went into the water for a few hours, chiefly to drink, but sometimes also to take a little food.

Hydromedusa, a South American genus, has a neck even longer than that of Chelodina, which it much resembles externally. But the nuchal shield, large and broad transversely, is situated behind the anterior marginals, looking therefore like a sixth neural shield. The neural plates form a continuous row, only the last pair of costal plates meeting in the middle line. H. tectifera occurs in Southern Brazil, and in the La Plata. The shell is dark brown above; yellowish, with dark spots, below; the head and neck are olive-coloured, adorned with a broad white, black-edged band on either side. Fore- and hind-limbs broadly webbed, and with four claws. Total length of the shell about eight inches.

Fam. 3. Carettochelydidae.–The shell is covered with soft skin instead of horny shields. The limbs are transformed into paddles, with elongated digits, and have only two claws. The neck is short, and not retractile. In other respects the skeleton, notably the plastron, pelvis, and skull, conform with the Pleurodirous type. Only one species, Carettochelys insculpta, still imperfectly known, from the Fly River, New Guinea. Length of the shell of the only complete specimen about 18 inches. This peculiar creature seems to stand in the same relation to the typical Pleurodira, as do the Chelonidae to the Testudinidae, except for the complete reduction of the horny shields upon the shell, recalling in this respect Sphargis and Trionyx.

Sub-Order 3. Trionychoidea.–The shell is very flat, oval, or almost round, and is covered with soft, leathery skin instead of with horny shields. The limbs are broadly webbed, and only the three inner digits are provided with claws. Carnivorous, found in the rivers of Asia, Africa, and North America.

The head and neck are completely retractile, bending by a sigmoid curve in a vertical plane like that of the Cryptodira. The jaws are concealed by soft, lip-like flaps, and the nose forms a soft short proboscis. The ear is hidden. The skull, Fig. 91, is flat, with three long posterior processes, formed by the supra-occipital above, and the squamosals on either side. The whole temporal region forms a wide, shallow fossa, without any indication of being arched or bridged over. The premaxilla is extremely small, unpaired, not even reaching the nasal cavity or the vomer. The maxillaries are correspondingly enlarged, surrounding the choanae, which are separated by the narrow vomer. The palatines form a median suture, and are joined behind by the long basisphenoid, which separates the long pterygoids from each other. The quadrate is trumpet-shaped, with a posterior notch for the stapes. The zygomatic arch is complete, and is formed by the quadrato-jugal and the jugal; the latter joins the maxillary and postfrontal, mostly reaching the orbit; in some cases it also just meets the parietal, thereby adding to the strength of the postorbital arch. The prefrontals are large; nasals are absent. The mandible is remarkable for the great development of the coronoid process.

The pubic and ischiadic bones enclose a large heart-shaped foramen, and are free from the plastron; the ilia are attached only to the sacral ribs. The carapace is peculiar in so far as it is very incomplete peripherally, the ribs extending considerably beyond the costal plates, nor are they joined by marginal plates, which are absent, unless they are represented by a few small ossifications imbedded in the posterior marginal flap of the disc (Emyda of India). The rim of the disc is always formed by a horizontal, cutaneous, very flexible flap. All the dorsal plates have a rough upper surface, vermiculated or rugose, as usual with such dermal bones, which have lost most of or all their horny covering, and have sunk more deeply into the skin. The nuchal plate has usually a pair of rib-like processes. The neurals form a continuous series, except in the African Cyclanorbis, in which they are much reduced in size, and separated by the costal plates.

The plastron is imperfect, all its constituent nine elements being only loosely connected with each other, and there remains a wide median vacuity between the lateral elements. Most of these plastral bones are reduced to splints, which, instead of meeting by regular sutures, loosely interdigitate with their jagged edges. In the young all these ventral elements are deeply imbedded in the soft, leathery skin, and they do not at all resemble in appearance those of the dorsal side. With age they develop upon their ventral surface stronger and denser ossifications, which ultimately broaden out, sometimes beyond the original underlying bone, and assume the characteristic vermiculated surface-appearance. This is undoubtedly a process of exostosis, a step towards revival of that armour which had been much reduced ancestrally. To appreciate this condition, it is at least suggestive that these mud-tortoises, when kept in the usual hard-bottomed tanks, invariably become sore, the skin wearing through where the imbedded plastral bones touch the ground. Thus what is crammed into the short life of a captive individual, is in the natural course of events spread over many generations, whereby it has ceased to be pathological, and has become a comparatively new, tertiary, but regular feature.

It is not open to much doubt that the characteristic features of the Trionychoidea are not primitive but secondary. This is indicated by the whole structure and behaviour of the carapace and plastron. The softening of the whole shell, the loss of the horny shields, the reduction of the claws, are the direct and almost unavoidable results of life in muddy waters.

Geologically they do not seem to be very old. They appear, already referable to the genus Trionyx, in the Upper Cretaceous strata of North America. In the Lower and Middle Tertiary strata many species existed in North America and in Europe, and it is of great importance that in these species the costal plates were much broader, and the marginal plates better developed, than in the recent forms. Now their half-dozen genera, with about twenty-four species, are confined to North America, the tropical and warmer parts of Asia, and the Malay Islands, and to Africa from the Nile to the Senegal and to the Congo.

The habits of Trionychoidea have found few observers. According to L. Agassiz,^[138] they live in the muddy bottom of shallow waters, burying themselves in the soft mud, with only the head, or a small part of it, exposed. They breathe without moving the body, by raising up the long neck and carrying the leathery snout above water. When moving through the water they strike horizontally with both pairs of limbs, alternating, however, the right and left; but when they start suddenly, the front limbs are seen moving together towards the tip of the snout, and then striking simultaneously backward with great power. As the shield does not project forward, the fore-limbs usually move beyond the shield, and as its outer edge is sharp, and the feet are broad, their webs reach above as well as below the plane of that edge, so that the water is driven partly over and partly under it. When they move along the bottom, the limbs still move horizontally, the webs striking against the water, and the inner toes, those with the claws, against the bottom. They also bury themselves horizontally, becoming covered by only a thin layer of mud. They readily resort to the shell for protection. The neck and head are withdrawn entirely, the loose skin rolling off from the greater part of the neck; and the skin of the legs also slips off, as far as the elbows and knees. In confinement they exhibit great quickness; their movements are abrupt and unsteady, except when they swim rapidly in one direction. They then dart their long and slender neck quickly forwards or sideways and upwards, as snakes do, and bite in the same way, striking suddenly. Their temper is bad or even ferocious, and large specimens are quite dangerous.

Their food consists of all sorts of aquatic animals, fish, frogs, and molluscs, for instance Anodonta and Paludina. According to the different diet, many species develop a peculiar kind of dimorphism, a reasonable explanation of which has been given by Boulenger. In the young the horny coverings of the jaws are sharp, with cutting edges, and in those specimens which keep to a diet of fish and other soft creatures, the jaws remain in the same condition. But in those which take to living upon molluscs, the hard shells of which they have to crush, the horny edges are worn down; and broad, thick, horny, crushing pads are developed in their stead, the supporting parts of the jaws becoming more massive. The masticatory muscles are likewise enlarged, and a tubercle grows upon the lower border of the jugal bone, whence arises part of the masseter muscle.

The eggs are round, thick-shelled, but very brittle; they are laid in the sand above the level of the water, and this is the chief occasion on which these tortoises creep on land.

Trionyx.–The plastron has no special cutaneous valves for the concealment of the hind-limbs. This is the principal genus, with the greatest number of species and the widest distribution, the latter coinciding with that of the whole family. The upper surface of the shell of young specimens frequently forms numerous longitudinal ridges or series of little horny tubercles which disappear with age.

T. ferox, the commonest "Soft-shelled Turtle" of the United States. Olive above with scattered, small, round, black spots; young with conical, spine-like tubercles, especially on the nuchal border and on the posterior portion of the shell, which has a pale, black-edged border. A light, black-edged streak passes through the eye and joins its fellow on the snout. The limbs are olive brown, spotted and marbled with black. The under parts of the shell are white. Very large specimens have a shell 18 inches in length and 16 inches wide. Holbrook gives the following account of its habits:–

"A voracious, carnivorous creature. They reside most constantly in the water, swim with rapidity, and choose for their retreat holes under the banks of rivers, or under rocks; and not unfrequently the trunk of some huge forest tree, fallen into the stream, affords them shelter. Sometimes they leave the water and conceal themselves in the mud: I have frequently seen them thus buried to the depth of 2 or 3 inches, leaving only a small breathing hole for the long neck and narrow head, which is occasionally thrust out, but most commonly it is retracted so that one would pass near without observing their habitation; and if seen, it might easily be mistaken for the residence of some large insect. At other times they may be seen in numbers on rocks in shallow water, basking in the sun, apparently asleep. They bite severely when provoked, darting forward with great velocity the long neck and head, and not unfrequently spring upward at the same time and make a loud hiss.

In the month of May the females seek sandy places along the banks of the waters they inhabit to lay their eggs, generally about sixty in number; and it is remarkable that, though their motions are slow and difficult on dry land, yet at this season they sometimes mount hillocks several feet high. The flesh affords the most delicate food, surpassing that even of the Green Turtle. The geographical distribution is interesting. It inhabits the Savannah as well as all those rivers that empty into the northern borders of the Gulf of Mexico; it ascends up the broad Mississippi, and is found in all its tributaries, even to the very foot of the Rocky Mountains; it abounds in the chain of great northern lakes both above and below the Falls of Niagara, and is common in the Mohawk, a tributary of the Hudson river; but it is not found in any other Atlantic stream between that and the Savannah river, a distance of nearly 800 miles."

T. triunguis, the only African species, ranging from the Senegal and Congo into the Nile-system, but occurring also in Syria, is perhaps the largest of all Trionychidae, reaching a shell-length of almost 3 feet. The adults are olive-brownish above, the throat and under parts of the shell with round, white spots separated by a dark network. The young have whitish specks and spots.

T. gangeticus and T. hurum are the principal Indian species. The former is the larger of the two, with a shell of more than 2 feet in length; olive above, the young with fine black vermiculations; head with a black longitudinal streak from between the eyes to the nape, intersected by two or three chevron-shaped black streaks; under parts yellowish. T. hurum is olive brown above and below, in younger specimens with conspicuous, large, yellow spots on the sides of the head. The young are ornamented with two or three pairs of large round spots on the back, and the same applies to the beautiful young of the Burmese, T. formosa.

The three genera, Cycloderma and Cyclanorbis of Tropical Africa, and Emyda of India, have a pair of cutaneous femoral valves or flaps on the plastron, beneath which the hind-limbs are withdrawn.

CHAPTER X

DINOSAURIA–CROCODILIA

Sub-Class V.–DINOSAURIA.

The Dinosaurs begin and end with the Mesozoic epoch, and have a world-wide distribution. The name, "terrible Reptiles," refers to the gigantic proportions which many of them attained, not a few of them surpassing in size and shape the fantastic pictures of the dragons of our fables. Although these creatures came to an end millions of years before the first man-like beings appeared, it is reasonable to suppose that the widely-spread myths of dragons are based upon the accidentally disclosed skeletons of these monsters.

The skull is built after a plan which may be derived from a combination of the Crocodilian and Rhynchocephalian skulls, but the detail varies considerably in the many and much diversified members of this large sub-class. There is as a rule a pre-orbital foramen, which is smallest in the Ornithopoda. The orbit is completely encircled by bones, and the temporal fossa is divided by a squamoso-postfrontal or post-orbital bridge into a smaller supra-, and a much wider infra-temporal portion, the latter being bordered below by the jugal and quadrato-jugal, and this is firmly connected with the quadrate by an ascending process. The quadrate is long, more or less vertical in position, slanting either forwards or backwards, and firmly fixed above by the squamosal, perhaps also by a supra-temporal bone. The orbit is bordered by the jugal, lacrymal, pre- and post-frontals. The interparietal foramen seems to be abolished. Teeth, mostly alveolar and laterally compressed, are restricted to the dentary, maxillary, and premaxillary bones. In the Orthopoda the latter carry no teeth, or these are restricted to the lateral portion, leaving a wide diastema. This toothless part plays upon a peculiar crescent-shaped bone, the so-called predentary, which rests loosely upon the anterior ends of the mandibular rami, which latter do not as a rule form an osseous symphysis. The Ceratopsia possess in addition a similar upper toothless piece, the prerostral, a kind of pre-premaxilla. The morphological value of these extra pieces is quite obscure; they were in all probability provided with thick, horny pads. The bones of the roof of the mouth recall in their arrangement that prevailing in the Rhynchocephalia and the Parasuchia. There are two pairs of large vacuities; one between the maxillae, ectopterygoids and palatines; the other between the latter, the maxillae and the usually small or slender vomers. The pterygoids are perhaps the largest bones, and form a rather long symphysis; laterally and behind they abut against the quadrate, anteriorly against the ectopterygoids and the palatines, which latter they sometimes separate. A peculiar feature of some skulls, e.g. Ceratosaurus and Triceratops is the great size of the groove in which the large hypophysis of the brain is lodged.

The vertebrae are very variable, amphicoelous, opisthocoelous, nearly plain, with a slight concavity behind, or occasionally procoelous in the anterior region of the tail. Besides the usual pre- and post-zygapophyses many Sauropoda and Theropoda possess on the posterior trunk-vertebrae additional joints, effected by a vertical wedge, the hyposphene, which extends backwards from between the post-zygapophyses and fits into a notch between and below the anterior zygapophyses of the next following vertebra. These additional articulations are analogous to the zygosphenes and zygantra of snakes and iguanas, except that in these Sauria the wedges are formed on the opposite, namely the anterior ends of the vertebrae. The vertebrae of the neck and trunk are devoid of intercentra, but those of the tail carry long chevron-bones. The number of sacral vertebrae is generally increased to four or five. The ribs have well-developed capitula and tubercula, and the former have the tendency to shift from the centra or from their parapophysial processes on to the usually much elongated diapophyses of the neural arches. This arrangement, recalling the Crocodilian condition, results in an increased capacity of the dorsal portion of the body-cavity. Intervertebral articulation of the ribs does not occur except sometimes in the sacral region. Abdominal ribs are rare, but they occur in some of the Theropoda, e.g. in Compsognathus.

The sternum seems to have been mainly cartilaginous, with a pair of irregular, disc-shaped ossifications. How the coracoids were attached is unknown; they are small, generally with a foramen, but the scapulae are always very strong and slant backwards. Clavicles and interclavicles seem to be absent.

The fore-limbs are as a rule powerful, although often much shorter than the hind-limbs, which are then enormously developed, and in many genera of two of the main groups show a tendency towards a semi-erect gait. Some of the Dinosaurs, e.g. Iguanodon and Brontozoum, were absolutely bipedal. Others seem to have hopped like Kangaroos. In correlation with this more or less erect mode of progression the iliac bones are very strong, much elongated horizontally, and attached to more than three, often to five or even more, vertebrae. The pubic bones show two main types. Each consists either of a single strong shaft, which is connected distally with its fellow; or (Orthopoda) this main shaft sends out, below its point of contact with the ischium, a long process, the so-called post-pubis, which is directed downwards and backwards. In the latter case it runs parallel and in close contact with the ischium. Such bifurcated pubic bones never meet in the middle line. The ischia, on the other hand, are always connected with each other, not so much by fusion as by syndesmosis.

The hind-limbs exhibit all stages from a simple, plantigrade and five-toed state to a decidedly digitigrade, four, and even three-toed arrangement. Many genera exhibit the tendency to form an intertarsal joint, a feature elsewhere known in birds only, where it is typical and universal. The astragalus sends up an ascending process which tends to fuse with the anterior aspect of the distal end of the tibia, and the calcaneum is sometimes more or less firmly attached to the fibula. In Compsognathus even the distal tarsalia have begun to fuse with the metatarsalia, so that this reptile at least has a typical intertarsal joint. The femur is remarkable for the frequent possession of a "fourth" trochanter on the middle of the inner aspect of the shaft, undoubtedly for the insertion of the long caudi-femoral or long adductor muscle.

Many Dinosaurs possess hollow instead of solid bones. The vertebrae have large cavities in the Sauropoda, notably in Brontosaurus; in many Theropoda, e.g. Coelurus, Anchisaurus, Compsognathus, the limb-bones and the vertebrae are hollow, the latter being reduced to thin-walled shells with a few inner partitions, the bones being at the same time much swollen and enlarged. In the Ornithopoda the vertebrae are solid, but the limb-bones are hollow. The reason of this hollowing out is not easily found. Undoubtedly it results in a saving of material and weight, whilst at the same time, without loss of strength, the surfaces for the attachment of the necessarily powerful muscles are increased. But Compsognathus is a small, Brontozoum a gigantic, creature. On the other hand, the bones of the huge Stegosauri are solid. Most probably these cavities were, as in birds, filled with air-sacs ultimately in communication with the lungs; and it is by no means a baseless suggestion of Haeckel's that the Dinosaurs were warm-blooded. Their mode of propagation can only be guessed at from the circumstance that a rather well-preserved specimen of Compsognathus contains in its abdomen what may possibly be an embryo. There is nothing against the assumption that the Dinosaurs were viviparous; on the contrary, it seems more natural than that, for instance, an Atlantosaurus of more than 100 feet in length and many tons in weight, should have laid eggs.

Some of the herbivorous Dinosaurs, namely, the Stegosauri and the Ceratopsia, had a dermal armour of variable extent; the plates were loosely imbedded in the skin, and reached their greatest size along the middle of the back and tail, and these crested plates were probably covered with horny scutes, obviously weapons of defence. The Ceratopsia were armed with a pair of huge pointed horns on the head, and a smaller one on the nose (see Fig. 102, p. 430). It is difficult to guess the use of the weapons of these terrestrial monsters, unless they were employed against the equally large carnivorous Dinosaurs or in the combats for the possession of their charming mates.

About the ancestry of the Dinosaurs we know nothing except that their affinities lie with the Crocodilia; but it is impossible to derive either from the other. The oldest forms, in the present state of our knowledge–those which have left their three-toed spoors in the Trias of Connecticut–were already much specialised by having attained to an upright bipedal gait, while the Sauropoda, which except for their gigantic size are the most generalised, are of comparatively recent date, none of them being known from strata older than the Upper Jurassic. Twenty years ago, until the discoveries of numerous kinds in the United States, our knowledge of the whole group was very limited. There is a widely spread notion that the birds have sprung from some Dinosaurian stock. Huxley was the first to show clearly that birds were an offshoot of the reptiles, and he said of the Dinosaurs, especially his Ornithoscelida (Iguanodon, Scelidosaurus, Megalosaurus, Compsognathus, and others), that they "present a large series of modifications intermediate in structure between existing reptiles and Aves." Baur proved to his own satisfaction that we have to look for the ancestors of the Ratitae among the herbivorous Dinosaurs, especially the Ornithopodous forms, whilst the Carinatae are descendants of the Ratitae. However, even he had to give up this absolutely unwarrantable view.

It is easy to select a considerable number of characters amongst the various Dinosaurs which also occur in birds, and some of these have until a recent date been considered as peculiar to birds. For instance, the double, bifurcated pubic bones of the Orthopoda; the increased number of vertebrae to which the horizontally elongated ilia are attached, especially in the forms with an upright gait, and the bipedal feature itself; the possession of an ascending process of the astragalus and its fusion with the tibia in Compsognathus and Ceratosaurus among the Theropoda, and in Ornithomimus; the attachment of the distal tarsalia to the metatarsalia, e.g. in Compsognathus,–in fact, the formation of an intertarsal joint, a feature otherwise characteristic of, and peculiar to, birds; the frequent reduction of the fifth metatarsal bone; the backward position of the hallux and the proximal reduction of its metatarsal in Compsognathus; the elongation and partial fusion of the functional metatarsals in the latter genus and in Ceratosaurus; the regular increase of the phalangeal numbers of the first four toes from two to five in many of the Ornithopoda;–in short, the great resemblance between the feet of some of the Dinosaurs and those of the birds. However striking these arguments are, they are instances of convergent analogies. The upright walk, which has been assumed and improved upon independently by members of both Theropoda and Orthopoda, has produced the same, or nearly the same modifications in them as in the birds.

It is easy to show that these features are mere coincidences. The oldest bird known is Archaeopteryx from the Upper Oolite of Bavaria. Consequently all those Dinosaurs, which are of the same and of later date, have to be excluded from the supposed ancestry, and they happen to be those in which (as in Ceratosaurus, Compsognathus, Ornithomimus, Iguanodon) the resemblances are greatest. There remains only Anchisaurus of the Upper Trias, more or less contemporary with the Brontozoum, which left its three-toed footprints (Archaeopteryx has four well-developed toes) with Zanclodon. Moreover, the most bird-like foot is either that of the Theropoda, which, like Anchisaurus and Zanclodon, differ from birds by the formation of the pelvis, or of some of the latest Ornithopoda. What, then, is the good of selecting a number of bird-like features from members of Dinosaurs which we are bound to class in different groups, and which existed, some in the lower, others in the middle, or even in the latest Mesozoic periods?

Lastly, the advocates of the Dinosaurian ancestry of birds cannot have fully appreciated the enormous differences between the wing of Archaeopteryx and the fore-limb of any Dinosaur with the most avian resemblances in the hind-limbs. The fore-limbs of these reptiles are modified in a direction diametrically opposed to that from which a bird-like wing could be developed. The skull presents another difficulty,and here again Compsognathus, a contemporary of Archaeopteryx, comes perhaps nearest to that of a generalised bird's skull. The ancestors of the birds must have combined the following characters:–Of not later than Mid-Oolitic age, with bifurcated pubic bones, four functional toes, elongated metatarsals, complete clavicles, premaxillary teeth, and free, not firmly fixed quadrate bones. But such creatures are not Dinosaurs.

We divide the enormous number of Dinosaurs according to the formation of the pelvis, that of the hind-limbs, and the dentition, into four orders.

Order I. SAUROPODA.

Pubes simple, with symphysis. Premaxillae with teeth. Plantigrade.

The teeth are mostly spatulate, laterally compressed, with sharp edges, but without serrations. Skull with a pair of large pre-orbital fossae. The centra of the vertebrae of the trunk have large lateral cavities. The fore- and hind-limbs are pentadactyle, plantigrade, and hoofed, of the typical walking type; the bones of the limbs are stout and solid; the femur is devoid of an inner distal or fourth trochanter. The carpal and tarsal bones are free. Herbivorous. The Sauropoda comprise some of the most gigantic terrestrial creatures which have ever existed, compared with some of which the bulk of an elephant appears almost insignificant. Their range in time extends from the Lower Oolite into the Cretaceous, with a perhaps world-wide distribution, namely, Western Europe, North America, Patagonia, Madagascar, and India. Although they are, except for their size, the least specialised of all Dinosaurs, none of the Sauropoda hitherto discovered are old enough to claim to be the ancestors of the other Dinosaurs.

Brontosaurus excelsus of the Upper Jurassic of Wyoming was a giant at least 60 feet long and about 10 feet high. The head is extremely small in proportion, not so broad as the fourth of the thirteen vertebrae of the long and flexible neck. The trunk is comparatively short, the tail longer than the neck, and provided with numerous chevron-bones. Most of the vertebrae are hollow, especially the five co-ossified sacrals. The spinal canal of the sacral region is very wide, indicating a strong sacral swelling in conformity with the huge posterior limbs. The pubic bones are stronger than the ischia. The long axis of the former stands almost vertically like that of elephants, and the knee is scarcely bent in the erect position. The shoulder-girdle consists of long scapulae, broad at the base and small, almost square and perforated coracoids, which latter fit into a pair of partly ossified plates representing the sternum.

Atlantosaurus immanis of the Upper Jurassic of Wyoming and Colorado, is supposed to have been 115 feet long, perhaps the biggest and bulkiest of all animals, the femur measuring more than 6 feet in length and 2 in width at the upper end.

Morosaurus grandis, of the Upper Jurassic of Wyoming, with allied forms in the Purbeck and Wealden of England, reached a length of 30 feet; in general appearance resembling Brontosaurus, but the sacrum consists of four vertebrae only, and the ischia are bent backwards in their distal halves, so that their symphysis is formed by the shafts instead of by their ends.

Ornithopsis and Cetiosaurus, likewise huge creatures, from the English Wealden and from the Great Oolite respectively, are rather imperfectly known, although several species of each, under many generic synonyms, have been described.

Diplodocus longus, of the Upper Jurassic of Colorado and Wyoming, is almost completely known. More than 40 feet long, it had a head in its general outlines not unlike that of a horse, the skull being about two feet long. The outer nasal openings are confluent, elongated, and lie far back on the top of the skull. There is a pair of large antorbital, and a pair of smaller lacrymal fossae. The teeth, long and slender, are restricted to the anterior portion of the mouth, with many successors, which, decreasing in size, lie on the inner or lingual side of the functional tooth, like the cartridges in a repeating rifle. The functional teeth themselves are implanted in sockets. The generic name refers to the peculiar chevron-bones, each half of which diverges into an anterior and a posterior branch.

It is difficult to understand how these huge, long-necked Sauropoda lived and moved about. The long neck suggests at first sight predacious habits, but the teeth, rather feeble in Diplodocus, and distinctly of the plant-cutting type in other genera, put this out of the question. The high position of the unpaired nasal opening, and the shortened nasal bones of Diplodocus, are features indicative of aquatic habits, but the short-toed, plantigrade limbs are absolutely adapted to terrestrial life, and we cannot well assume that such enormous brutes as Atlantosaurus could possibly have ventured into swampy ground.

Order II. THEROPODA.

Pubes simple, with symphysis. Premaxillae with teeth. Digitigrade. Carnivorous.

The teeth are pointed, recurved, laterally compressed and serrated. The nasal openings are large, lateral, and nearly terminal. The vertebrae and the large bones of the limbs are hollow. The fore-limbs are considerably shorter than the hind-limbs, which are distinctly digitigrade, many of the species having a pronouncedly upright gait. The proximal tarsalia show a tendency to fuse with the tibia, and the astragalus has sometimes an ascending process, by which the fusion with the tibia is strengthened. The first and fifth metatarsals are often reduced, while the three middle bones are elongated and sometimes even fused with each other, so that the whole foot assumes a striking resemblance to that of birds. The terminal phalanges are protected by curved claws. Owing to the shortness of the fore-limbs, and the often considerable length of the hind-limbs, which are strongly bent at the knee and the ankle-joint, these animals must have progressed somewhat like clumsy kangaroos.

The Theropoda, of which a great number of genera are now known, from the size of a slender cat to that of an elephant, lived from the Upper Trias to the Upper Oolite, both in Europe and in North America.

Brontozoum giganteum, one of the oldest forms, is known from its foot-spoors only, which, together with other three-toed spoors in the sandstone of the Connecticut valley, were originally described and figured by Hitchcock as Ornithichnites (ἴχνος = track, or spoor). Some of these imprints are more than a foot in length, the right and left spoors following alternately at a distance of from four to six feet. In some cases the long trailing tail has left a furrow behind, and the large tracks are accompanied or crossed by much smaller, and even by quite tiny tracks, otherwise similar, and undoubtedly made by the young.

Anchisaurus, from the same locality, was still Sauropodous, in so far as the metatarsals are still free, with two, three, four, and five phalanges on the first four toes, but the fifth metatarsal is reduced, carrying a vestige of only one phalanx, and the proximal tarsal bones are fused with the tibia and fibula respectively. Total length some seven feet, of which about four belong to the tail.

Zanclodon, from the Keuper of Würtemberg, about ten feet long, with pentadactyle hands and feet. Ischia stronger than the pubic bones, which are distally much broadened. The femur is nearly three feet long, and possesses a fourth trochanter. The astragalus has an ascending process, and is fused with the tibia. The toes are short, strong, and clawed. The shoulder-girdle and fore-limb are strong, the latter well adapted to grasping. The teeth are much compressed laterally, with sharp, finely serrated edges. Several allied genera have been described from the Upper Trias of France and England: others from corresponding strata of India and South Africa.

Megalosaurus, from the Trias to the Wealden in England and France, with other species in Colorado and India, reached a considerable size, larger than that of any other Theropoda, the scapula of M. bucklandi being nearly three feet long, and the femur still longer. The hind-limbs are twice as long as the fore-limbs. The cervical vertebrae are short, the neck being much shorter than the tail. Hands with five fingers, feet with four toes. Pubic bones long and slender, with a broad symphysis. With well-developed abdominal ribs, resembling those of crocodiles.