broad bodies and two pairs of limbs of which the hinder are longer and stronger. Though there are no scales nor pectoral plates, portions of the skin of the back are in some cases ossified. They are typified by the frogs and toads. They are only found fossil in younger Tertiary deposits.

iii. Peromela or snake-like amphibians-animals with serpentiform bodies without limbs. They are not known as fossils.

iv. Labyrinthodonta — animals now entirely extinct which possessed bodies somewhat like those of the salamanders, with relatively weak limbs and long tail. The head was defended by hard plates of bone, the breast by three sculptured bony plates, and the lower side of the body by an armour of oval plates or scales. The feet appear to have been five-toed. The footprints of these creatures were first found; but more or less perfect skeletons of them have since been obtained. Their name is taken from the labyrinthine structure of their large teeth. The earliest known Labyrinthodonts are from the Carboniferous system; they formed the magnates of the world until they were supplanted in early Mesozoic time by the great development of Reptilians (Fig. 163). REPTILIA or true reptiles, with horny scales or bony scutes, are represented now by turtles, tortoises, snakes, lizards, and crocodiles, but flourished formerly in many remarkable forms which have long been extinct. Embracing all the known living and extinct types in one view we may group them into the following orders :

i. Chelonia-the tortoises and turtles, distinguished for the most part by the bony case or box in which the body is enveloped. As many of these animals are of aquatic habits their hard parts must often be covered up and preserved in sedimentary deposits. They are not uncommon in the fossil state, as far back as the Jurassic series.

ii. Ophidia-snakes and serpents, covered with horny scales, and remarkable for the number of their vertebræ (which, in some pythons, amount to more than 400), and for the want of limbs. They are not known fossil except in the Tertiary formations.

iii. Lacertilia-lizards, chamæleons. The oldest forms occur in the Permian system (Protorosaurus); in the Triassic period lived the Rhyncosaurus, Hyperodapedon, and Telerpeton (Fig. 168); in the Cretaceous, the long-necked Dolichosaurus and the gigantic Mosasaurus.

iv. Crocodilia-the crocodiles, alligators, and gavials form the highest type of living reptiles. The earliest trace of them in a fossil state is in the Stagonolepis of the Trias (Fig. 169). They abounded in the Jurassic seas, the genera Teleosaurus and Steneosaurus being conspicuous, while in Cretaceous time the Goniopholis abounded. None of the modern crocodiles, however, are truly marine.

The following orders of reptiles are now wholly extinct :v. Ichthyosauria-animals somewhat resembling whales in shape, the head being joined to the body with no distinct neck and the body tapering away behind. It appears to have been covered merely with skin and moved through the water by means of two pairs of paddles. In the huge head the most conspicuous feature was the large eye-orbits filled with a circle of bony plates that remain often well preserved. There is only one known genus, Ichthyosaurus, abundant in the Lias (Fig. 180).

vi. Plesiosauria-distinguished for the most part by the disproportionate length of the neck and the smallness of the head. Like the ichthyosaurs, the plesiosaurs appear to have had no bony covering upon their skin; they had two pairs of paddles, those behind being largest, and a comparatively short tail. The earliest plesiosaurus are found in Triassic rocks (Nothosaurus, Simosaurus, Pistosaurus), but they are most characteristic of the Jurassic formations (Plesiosaurus, Pliosaurus).

vii. Dicynodontia-lizard-like animals with crocodilian vertebræ and tortoise-like jaws which were probably cased in a horny beak. They have been found in certain supposed Triassic strata in Scotland, South Africa, and India (Dicynodon, Oudenodon). viii. Pterosauria, flying reptiles or Pterodactyls-distinguished by the length of their heads and necks, and the proportionately great size of their fore-limbs, on which the outer finger was enormously elongated to support a wing-like membrane. These animals no doubt flew from tree to tree and hopped or shuffled along the ground. They appear to have been confined to the Mesozoic periods. The important genera are Pterodactylus (Fig. 181), Rhamphorhynchus, Dimorphodon, and Pteranodon.

ix. Deinosauria a remarkable group of animals, mostly of enormous size, which presented structures linking them with birds. Some of them had a covering only of naked skin, others possessed an armour of bony plates like those of the crocodile. The hind-limbs are usually enormously developed in comparison with the fore-limbs, showing that the animals probably walked on their hind feet. The deinosaurs abounded during the Mesozoic ages and in many diverse types. Some of the more important genera are Iguanodon (Fig. 192), Hylaosaurus, Cetiosaurus, Megalosaurus, and Compsognathus. The largest animal yet known, the Atlantosaurus, has been found in the Jurassic rocks of North America (p. 399).

x. Thecodontia-a group of carnivorous reptiles, remarkable for possessing teeth which have been classed by Professor Owen as incisor, canine, and molar. Their remains have been found in supposed Triassic rocks in South Africa.

AVES, birds. This important section of the animal kingdom has been but sparingly found in the fossil state. The facility with which birds can escape by flight from the destruction that befalls other land-animals will no doubt suffice to explain why their fossil remains should be so infrequent. The oldest known birds had curious reptilian affinities, being furnished with jaws and teeth. Taking all the known forms of birds, recent and fossil, they may be grouped in the following subdivisions:

I. Saururæ in this singular extinct group the vertebral column was prolonged into a long lizard-like tail, each vertebra of which, however, bore a couple of quill-feathers. The only known example is the Archæopteryx of the Jurassic system-the oldest bird yet discovered (Fig. 182).

II. Odontornithes or toothed birds. Some of these (Odontolcæ) were diving birds with rudimentary wings, ratite sternum, powerful legs, a strong tail for steering, and jaws with numerous conical teeth sunk in a deep continuous groove (Hesperornis). Others (Odontotormæ) were provided with strong wings and carinate sternum, and had their teeth sunk in separate sockets, as in the crocodiles. The toothed birds have long been extinct. They have been found most abundantly in the Cretaceous rocks of Kansas. III. Ratitæ the cursores or running birds, such as the ostrich, cassowary, rhea, emeu, and apteryx. These have not with certainty been found fossil in strata older than the Tertiary series. The gigantic extinct Dinornis of New Zealand belongs to this class.

IV. Carinatæ generally possessing powers of flight. These include most of the birds of the present day. The arrangement of this great sub-class into definite orders has not been yet satisfactorily accomplished. The student, however, may find some advantage in making himself acquainted with the following names which, though in process of being superseded, are still in

common use.

Natatores-swimmers or palmipeds, with short legs placed behind and provided with webbed feet. These include gulls, penguins, geese, ducks, swans, cormorants, etc. Remains of this order are found in Cretaceous and Tertiary strata. Grallatores-waders, chiefly found by the shores of rivers, lakes, or the sea, distinguished by the length of their legs which are not completely webbed. They include plovers, cranes, flamingoes, storks, herons, snipes, etc. They have been found fossil in Cretaceous and Tertiary rocks. Rasores-scratchers or gallinaceous birds, including the various tribes of fowls and pigeons. They are found fossil in Tertiary strata. Scansores -climbers, including the parrots, cuckoos, toucans, and trogons. They are only found fossil in Tertiary and Post-tertiary rocks. Insessores-perchers, passerine birds include by far the largest number of living birds, and all the ordinary song-birds. They have not been met with in a fossil state in rocks older than the Tertiary series. Raptores or birds of prey comprising birds with strong, curved, sharp-edged and pointed bills, and strong talons, as the eagles, hawks, falcons, vultures, and owls. This order also has not been obtained fossil except in Tertiary and Post-tertiary rocks.

MAMMALIA. -The highest class of the vertebrata is represented chiefly on the land, the marine representatives being few in number, though often of large size (whales, dolphins, porpoises, manatee, seals, morse). In marine deposits, therefore, we need not expect to find mammalian remains abundant at the present time. Doubtless from the time of their first appearance mammals have always been on the whole terrestrial animals; their fossil remains consequently occur but sparingly among ancient geological formations. The earliest known examples belong to the Marsupial type, and have been found in the Triassic and Jurassic rocks of Europe and North America.

I. PROTOTHERIA or ORNITHODELPHIA--including the two types of Ornithorhynchus and Echidna.

II. METATHERIA or DIDELPHIA-Marsupial animals. Comprising the Opossums (Didelphide), Dasyures, Myrmecobius, Perameles, Kangaroos, and Wombats. As just mentioned, it is representatives of this section of the vertebrates that occur fossil among the Mesozoic rocks [Microlestes, Fig. 170, Dromatherium, Amphitherium, Phascolotherium, Fig. 183].

III. EUTHERIA or MONODELPHIA-including the vast majority of living and extinct mammalia. They may be grouped as follows :

Edentata-sloths, ant-eaters, armadilloes, pangolins, and African ant-eaters. Some enormous extinct types of Edentates have been found in America [Megatherium, Mylodon, Moropus, Glyptodon]. Sirenia-aquatic fish-like animals including the manatee, dugong, sea-cow. The last-named is now extinct, the last having been killed so recently as 1768. Numerous fossil remains of Sirenians occur in Miocene and Pliocene deposits of Europe [Halitherium]. Cetacea - whales including the Balænidæ or whalebone whales, Delphinoidea or toothed whales (Sperm whale, Ziphius, Narwhal, Porpoise, Ca'ing whale, Grampus, Dolphin). Cetacean earbones and other bones are not infrequent in Tertiary and Posttertiary strata.

Insectivora-small terrestrial mammals like the shrews, moles, myogale. No fossil insectivores older than Eocene times are known, except perhaps Stereognathus of the Stonesfield slate. Cheiroptera-animals with the fore-limbs adapted for flight, including the tribe of bats. Fossil representatives are found as far back as Eocene rocks.

Rodentia-small terrestrial plant-eating mammals, distinguished by their large chisel-shaped incisor teeth, specially adapted for gnawing, and by the absence of canines. Among them are squirrels, marmots, beavers, dormice, rats, mice, voles, lemmings, jumping mice, jerboas, porcupines, chinchillas, cavies, rabbits, and hares. Fossil rodents belonging to most of the existing families have been met with in Tertiary and Recent strata, together with some extinct types.

Ungulata or hoofed animals include the Hyrax, the Proboscideans (elephants, Fig. 205, and the extinct types of Mastodon, Fig. 199, Deinotherium, Fig. 200, etc.) and the extinct type of the Deinocerata (Fig. 196); the perissodactyl or odd-toed group (tapirs, rhinoceroses, horses [Palæotherium], Fig. 195), and the artiodactyl or even-toed group (hippopotamus, peccary, swine, llama, camel, chevrotains, the true ruminants, such as deer, antelopes, giraffes [Helladotherium, Fig. 203], and all bovine animals). The earliest known forms are of Eocene age.

Carnivora, so named from the majority of them subsisting on animal food and being eminently beasts of prey. They are divided into (1) Fissipedes or true carnivores, generally adapted for life on land, comprising (a) the Æluroids or cat-like forms (lions, tigers, cats, puma, jaguar, cheetah, civet-cat, ichneumon, hyæna, and various fossil forms found in Tertiary