B. Teeth rooted. Three upper incisors and a canine.

Hind

limbs not disproportionately large. Feet syndactylous, broad, with four subequal outer toes, and a large opposable hallux. Phalangerida.

7. Teeth rooted. Three upper incisors, and frequently a canine. Hind limbs disproportionately large, with syndactylous feet as in Peramelida. Macropodido.

Suborder POLYPROTODONTIA.

The leading characters of this group are given in the foregoing schedule. This group is the only one represented at the present day, and so far as we know also in past epochs, beyond the confines of the Australasian region and adjacent islands.

Family DIDELPHYIDÆ.

Incisors very small compressed pointed The last premolar

Dentition: i, c 1, p 3, m 4; total 50. and pointed. Canines large. Premolars with crowns. Molars with numerous sharp cusps. preceded by a deciduous multicuspidate milk-molar, which remains in place until the animal is nearly adult (Fig. 34). Limbs of moderate development, each with five complete and distinct toes, all of which are provided with short, compressed,

curved, sharp claws of nearly equal size, except the first toe of the hind foot or hallux (Fig. 37), which is large, widely separable from the others, to which it is opposed in climbing, and terminates in a dilated rounded extremity, without a nail. Tail generally long, partially naked and prehensile. Stomach simple. Cæcum of small or moderate size. Pouch generally absent, sometimes represented by two lateral folds of the abdominal integument, partially covering the teats, rarely complete. Vertebræ : C 7, D 13, L 6, S 2, C 19-35.

The Didelphyida, or true Opossums, differ from all other existing

FIG. 37.-Skeleton of the right hind

Marsupials in their habitat, being foot of the Virginian Opossum (Didelphys peculiar to the American continent.

marsupialis).

They are mostly carnivorous or insectivorous in their diet, and arboreal in habits.

Opossums occur throughout the greater part of the American

continent, ranging from the United States to Patagonia, the greater number of species being found in the warmer regions. In South America the opossums take the place of the Eutherian Insectivora, and the sharp cusps on their teeth are admirably adapted for crushing the insects on which they mainly subsist.

Chironectes. The family comprises two genera only, namely Didelphys, containing all the species, with the exception of the curious Yapock, which forms by itself the genus Chironectes, and is distinguished from all other Opossums by its webbed feet, non-tuberculated soles, and peculiar coloration. Its ground colour is light gray, with four or five sharply-contrasted brown bands passing across its head and back, and thus giving it a very peculiar mottled appearance. It is almost wholly aquatic in its habits, living on small fish, crustaceans, and water insects. Its range extends from Guatemala

to southern Brazil.

Didelphys.2 The type genus Didelphys is a very large one, containing, according to Mr. O. Thomas, twenty-three existing species. It may be divided into five groups, or sub-genera, all of which have received distinct names. The typical group is represented only by the common or Virginian Opossum (D. marsupialis), of which the numerous varieties have received separate specific names. This species is of large size, with a long, scaly, prehensile tail, and long bristle-like hairs mingled with the fur. The pouch is complete. It ranges over all temperate North America, and is also found in central and tropical South America, where it is commonly known as the Crab-eating Opossum. This animal is extremely common, being even found living in the towns, where it acts as a scavenger by night, retiring for shelter by day upon the roofs of the houses or into the sewers. The female produces in the spring from six to sixteen young ones, which are placed in her pouch immediately after birth, and remain there until able to take care of themselves.

As

The second or Metachirine group includes three species found all over the tropical parts of the New World. They are of medium size, with short close fur, very long, scaly, and naked tails, and less developed ridges on their skulls than in the type species. a rule there is no pouch adapted to carry the young, which commonly ride on their mother's back, holding on by winding their prehensile tails round hers. The Philanderine group is closely allied to the preceding, but is readily distinguished by the woolly hair, and the brown streak down the middle of the face. The Woolly Opossum (D. lanigera), which is represented in the accompanying woodcut (Fig. 38) carrying its young in the fashion mentioned above, is one of the two species of this group. In the

1 Illiger, Prod. Syst. Mamm. et Aves, p. 76 (1811).

2 Linn. Syst. Nat. Ed. 12, vol. i. p. 71 (1766).

fourth or Micoureine group the numerous species are all smaller than in the preceding groups, and have short and close hair, and no dark streak down the face. The best known species is the Murine Opossum (D. murina), little larger than a House-Mouse, and of a bright red colour, which is found as far north as central Mexico, and extends thence right down to the south of Brazil. The last or Peramyne group contains several extremely shrew-like species, of very small size, with short, hairy, and usually non-prehensile tails, not half the length of the trunk, and with wholly unridged skulls. The most striking member of the group is the Three-striped Opossum (D. americana), from Brazil, which is of a reddish-gray colour, with three clearly-defined deep-black bands

down its back, very much as in some of the striped mice of Africa.

The numerous fossil species of Opossum found in the Upper Eocene and Lower Miocene of Europe are of especial interest from a distributional point of view, since they indicate how the Opossums of America may have been connected with the Australian Marsupials. These forms were originally referred to Didelphys, but have been subsequently described as Peratherium and Amphiperatherium. The characters of the molar teeth on which these genera are based do not appear to be sufficiently important to justify their separation from Didelphys. Allied forms occur in the Tertiaries of North America, which were originally described under the name of Herpetotherium, but have been subsequently referred to Peratherium. Remains of many of the existing species of Opossum are found in a fossil condition in the Pleistocene cave-deposits of Brazil.

Family DASYURIDÆ

Dentition: i, c, p and m numerous, variable. Incisors small; canines well developed; molars with pointed cusps. Limbs equal. Fore feet with five subequal toes terminating in claws. Hind feet with the four outer toes well developed, and distinct from each other and bearing claws; the first (or hallux) clawless, generally rudimentary, sometimes entirely wanting. Stomach simple. No cæcum. Predatory carnivorous or insectivorous animals, inhabitants of Australia, Tasmania, and the southern parts of New Guinea and some of the adjacent islands. The aberrant genus Myrmecobius, though clearly a member of this family, is so sharply distinguished

FIG. 39.-The Thylacine (Thylacinus cynocephalus).

from all the others as to render a division into two subfamilies necessary.

Subfamily Dasyurinæ.-This comprises the more typical Dasyurida, in which the premolars and molars never exceed the normal number of seven on either side of each jaw, and in which the tongue is not specially extensile.

c,

Thylacinus.-Dentition: i, c 1, p 3, m446. Incisors small, vertical, the outer one in the upper jaw larger than the others. Summits of the lower incisors, before they are worn, with a deep transverse groove dividing them into an anterior and a posterior cusp. Canines long, strong, and conical. Premolars separated from one another by intervals, with compressed crowns, increasing in size from before backwards. True molars in general characters re1 Temminck, Monographies de Mammalogie, vol. i. p. 60 (1827).

sembling those of Dasyurus, but of more simple form, the cusps being not so distinct nor sharply pointed. Milk-molar very small, and shed before the animal leaves the mother's pouch. Humerus with an entepicondylar foramen. General form very Dog-like. Head elongated. Muzzle pointed. Ears moderate, erect, triangular. Fur short and closely applied to the skin. Tail of moderate length, thick at the base and tapering towards the apex, clothed with short hair. Hallux (including the metacarpal bone) wanting. Vertebræ : C7, D13, L6, S2, C 23. Marsupial bones represented only by small unossified fibro-cartilages.

The only known existing species of this genus, T. cynocephalus (Fig. 39), though smaller than a common Wolf, is the largest predaceous Marsupial at present living. It is now entirely confined to the island of Tasmania, although fragments of bones and teeth found in caves afford evidence that a closely allied species once inhabited the Australian mainland. The general colour of the Thylacine is

FIG. 40. Right lateral aspect of the skull of the Thylacine.

grayish brown, but it has a series of transverse black bands on the hinder part of the back and loins, whence the name of "Tiger" frequently applied to it by the colonists. It is also called "Wolf," and sometimes, though less appropriately, "Hyæna." Owing to the havoc it commits among the sheepfolds, it has been nearly exterminated in all the more settled parts of Tasmania, but still finds shelter in the almost impenetrable rocky glens of the more mountainous regions of the island. The female produces four young at a time. The pouch opens backwardly, and there are four The figure of the skull exhibits the peculiar Dog-like form so characteristic of the genus.

mammæ.

Sarcophilus.1-Dentition: i, c, p, mt. Upper incisors nearly equal, and placed vertically, the first not differentiated from the rest. Premolars rounded and closely crowded between the canine and molars, with broad crowns; molars broad and heavy, the last one without a distinct hind talon. Form thick and powerful;

1 F. Cuvier, Hist. Nat. des Mammifères, iv. (1837).