CHAPTER VI

THE SUBCLASS METATHERIA OR DIDELPHIA

_General Characters._—The Metatheria or Didelphia are represented at present by numerous species, presenting great diversities of general appearance, structure, and habits, although all united by many essential anatomical and physiological characters, which, taken altogether, give them an intermediate position between the Prototheria and the Eutheria.

Although the striking differences in external form, in many anatomical characters, and in mode of life of various animals of this section might lead to their division into groups equivalent to the orders of the Eutheria, it is more convenient on the whole to adhere to the usual custom of treating them all as forming one order called MARSUPIALIA,[37] the limits of which are therefore equivalent to that of the subclass. The more essentially distinctive characters are as follows.

In the structure of the brain and the presence of epipubic bones they agree with the Prototheria, while in the structure of the ear-bones and the shoulder-girdle and the presence of teats on the mammary glands they resemble the Eutheria, the reproductive organs belonging to neither one nor the other type, but having a special character representing an intermediate grade of development. The ureters open into the base of the bladder. The oviducts are differentiated into uterine and Fallopian portions, and open into a long and distinct vagina, quite separate from the cystic urethra. The penis is large, but its crura are not directly attached to the ischia. The spongy body has a large bifurcated bulb. The young are born in an exceedingly rudimentary condition, and are never nourished by means of an allantoic placenta, but are transferred to the nipple of the mother, to which they remain firmly attached for a considerable time, nourished by the milk injected into the mouth by compression of the muscle covering the mammary gland. They are therefore the most typically mammalian of the whole class. The nipples are nearly always concealed in a fold of the abdominal integument or “pouch” (marsupium) which serves to support and protect the young in their early helpless condition.

Entering more fully into the characters of the subclass, which are also those of the order Marsupialia, it may be observed that the brain is generally small in proportion to the size of the animal, and the surface-folding of the cerebral hemispheres, though well marked in the larger species, is never very complex in character, and is absent in the medium-sized and smaller species. The arrangement of the folding of the inner wall of the cerebrum differs essentially from that of all known Eutheria, the hippocampal fissure being continued forward above the corpus callosum, which is of very small size. The anterior commissure is, on the other hand, greatly developed.

[Illustration: FIG. 34.—Teeth of upper jaw of Opossum (_Didelphys marsupialis_), all of which are unchanged, except the last premolar, the place of which is occupied in the young animal by a molariform tooth, represented in the figure below the line of the other teeth.]

The teeth are always divisible, according to their position and form, into incisors, canines, premolars, and molars; but they vary much in number and character in the different families. Except in the genus _Phascolomys_, the number of incisors in the upper and lower jaws is never equal. The true molars are very generally four in number on either side of each jaw. The chief peculiarity in the dentition lies, however, in the mode of succession. Thus there is no vertical displacement and succession of the teeth, except in the case of a single tooth on either side of each jaw, which is always the hindermost of the premolar series, and is preceded by a tooth having more or less of the characters of a true molar (see Fig. 34); this deciduous tooth being the only one comparable to the “milk-teeth” of the diphyodont Eutheria. In some cases (as in _Potorous_) this tooth retains its place and function until the animal has nearly, if not quite, attained its full stature, and is not shed and replaced by its successor until after all the other teeth of the permanent series, including the posterior molars, are fully in place and use. In others, as the Thylacine, it is very rudimentary in form and size, being shed or absorbed before any of the other teeth have cut the gum, and therefore quite functionless. It must further be noted that there are some Marsupials, as the Wombat, _Myrmecobius_, and the Dasyures, in which no such milk-tooth, even in a rudimentary state, has yet been discovered, possibly in some cases from want of materials for observation at the right stage of development.

Epipubic or marsupial bones are present in both sexes of nearly all species. In one genus alone, _Thylacinus_, they are not ossified. The number of dorso-lumbar vertebræ is always nineteen, although there are some apparent exceptions caused by the last lumbar being modified into a sacral vertebra. The number of pairs of ribs is nearly always thirteen. The tympanic bone remains permanently distinct. The carotid canal perforates the basisphenoid. The lachrymal foramen is situated upon or external to the anterior margin of the orbit, and there are generally large vacuities in the bony palate. The angle of the mandible is (except in _Tarsipes_) more or less inflected. The hyoid bones have always a peculiar form, consisting of a small, more or less lozenge-shaped basihyal, broad ceratohyals, with the remainder of the anterior arch usually unossified, and stout, somewhat compressed thyrohyals. There are two anterior venæ cavæ,[38] into each of which a “vena azygos” enters. In the male the testes are always contained in a scrotum, which is suspended by a narrow pedicle to the abdomen in front of the penis. The vasa deferentia open into a complete and continuous urethra, which is also the passage by which the urine escapes from the bladder, and is perfectly distinct from the passage for the fæces, although the anus and the termination of the urethro-sexual canal are embraced by the same sphincter muscle. The glans is often bifurcated anteriorly. In the female the oviducts never unite to form a common cavity or uterus, but open separately into the vagina, which at least for part of its course is double. The mammæ vary much in number, but are always abdominal in position, having long teats, and in most of the species are more or less enclosed in a fold of the integument forming a pouch or marsupium, though in some this is entirely wanting, and the newly-born, blind, naked, and helpless young, attached by their mouths to the teat, are merely concealed and protected by the hairy covering of the mother’s abdomen. In this stage of their existence they are fed by milk injected into their stomach by the contraction of the muscles covering the mammary gland, the respiratory organs being modified temporarily, much as they are permanently in the Cetacea—the elongated upper part of the larynx projecting into the posterior nares, and so maintaining a free communication between the lungs and the external surface independently of the mouth and gullet, thus averting the danger of suffocation while the milk is passing down the latter passage.

[Illustration: FIG. 35.—Front view of skull of _Sarcophilus ursinus_, showing polyprotodont and carnivorous dentition (_Quart. Journ. Geol. Soc._ vol xxiv. p. 313).]

_Distribution._—The existing species of Marsupials are, with the exception of one family (the _Didelphyidæ_), limited in geographical distribution to the Australasian region,[39] forming the chief mammalian fauna of Australia, New Guinea, and some of the adjacent islands. The _Didelphyidæ_ are almost purely Neotropical, one or two species ranging northwards into the Nearctic region. Fossil remains of members of this family have also been found in Europe and America in strata of the Eocene and early Miocene periods; and it is probable that at least many of the polyprotodont Mesozoic mammals noticed in Chapter IV. are referable to the Marsupialia.

[Illustration: FIG. 36.—Front view of skull of Koala (_Phascolarctus cinereus_), showing diprotodont and herbivorous dentition (_Quart. Journ. Geol. Soc._ vol. xxiv. p. 313).]

_Classification._—In dividing the Marsupials into minor groups, it may be observed that one of the most obvious distinctive characters among them is derived from the form and arrangement of the teeth. In certain species, as the Opossums, Dasyures, and Thylacine, the incisors are numerous, small, and subequal in size, and the canines large, as in the typical placental Carnivores (Fig. 35). To these the term “polyprotodont” is applied, and they are all more or less carnivorous in their habits. In others the central incisors are very prominent, and the lateral incisors and canines absent or subordinate in function (Fig. 36). These are called “diprotodont,” and they are all wholly or in great part vegetable feeders. In one group of these, the Wombats, there are but two incisors above and the same number below; but all the others, including the Kangaroos, Koalas, and Phalangers, have two functional incisors below and as many as six above, three on each side, but of these the first or central pair is the most fully developed.

Some hesitation has frequently been expressed as to whether the Polyprotodont and Diprotodont types are entitled to constitute distinct primary groups, owing to the presence of syndactylism among the _Peramelidæ_ in the former, as well as in the latter; but if Mr. O. Thomas is right in regarding this feature as acquired independently in the two groups we may safely adopt such a division. Taking various combinations into consideration, the existing Marsupials readily group themselves into six very natural families, the leading characters of which may be summarised as follows:—

_Order_ MARSUPIALIA.

_A._ POLYPROTODONTIA.—Incisors numerous, small, subequal. Canines larger than the incisors. Molars with sharp cusps.

α. Incisors ⁵⁄₄. Hind feet with the four outer toes subequal, distinct, and a well-developed opposable hallux. _Didelphyidæ._

β. Incisors ⁴⁄₃. Hind feet with four outer toes distinct. Hallux small or rudimentary, rarely opposable. _Dasyuridæ._

γ. Incisors ⁴⁻⁵⁄₃. Hind feet long and narrow. Fourth toe larger than the others. Hallux rudimentary or absent. Second and third toes very slender, and united in a common integument (syndactylous). _Peramelidæ._

_B._ DIPROTODONTIA.—Incisors not exceeding ³⁄₃, usually ³⁄₁ but occasionally ¹⁄₁. Central (first) upper and lower incisors large and cutting. Upper canines generally, and lower invariably, absent or small. Molars with bluntly tuberculated or transversely ridged crowns.

α. Teeth with persistent pulps. Incisors ¹⁄₁, large, scalpriform, with enamel on the outer surface only. No canines. Hind feet with four subequal outer toes, partially syndactylous, and with rudimentary hallux. _Phascolomyidæ._

β. 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. _Phalangeridæ._

γ. Teeth rooted. Three upper incisors, and frequently a canine. Hind limbs disproportionately large, with syndactylous feet as in _Peramelidæ_. _Macropodidæ._

_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.

Dentition: _i_ ⁵⁄₄, _c_ ¹⁄₁, _p_ ³⁄₃, _m_ ⁴⁄₄; total 50. Incisors very small and pointed. Canines large. Premolars with compressed pointed crowns. Molars with numerous sharp cusps. The last premolar 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.

[Illustration: FIG. 37.—Skeleton of the right hind foot of the Virginian Opossum (_Didelphys marsupialis_).]

The _Didelphyidæ_, or true Opossums, differ from all other existing Marsupials in their habitat, being peculiar to the American continent. 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._[40]—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._[41]—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 subgenera, 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.

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. As 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 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.

[Illustration: FIG. 38.—The Woolly Opossum (_Didelphys lanigera_).]

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_ ⁴⁄₃, _c_ ¹⁄₁, _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 from all the others as to render a division into two subfamilies necessary.

[Illustration: FIG. 39.—The Thylacine (_Thylacinus cynocephalus_).]

Subfamily =Dasyurinæ=.—This comprises the more typical _Dasyuridæ_, 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.

_Thylacinus._[42]—Dentition: _i_ ⁴⁄₃, _c_ ¹⁄₁, _p_ ³⁄₃, _m_ ⁴⁄₄ = 46. 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 resembling 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: C 7, D 13, L 6, S 2, 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 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 mammæ. The figure of the skull exhibits the peculiar Dog-like form so characteristic of the genus.

[Illustration: FIG. 40.—Right lateral aspect of the skull of the Thylacine.]

_Sarcophilus._[43]—Dentition: _i_ ⁴⁄₃, _c_ ¹⁄₁, _p_ ²⁄₂, _m_ ⁴⁄₄. 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; head disproportionately large for the body; muzzle short and broad; ears broad and rounded; tail of moderate length, and evenly hairy. Hallux wanting; soles of feet naked, without defined pads. Humerus with entepicondylar foramen.

This genus is now represented only by a single species (_S. ursinus_) found in Tasmania, where, from its ferocious and destructive habits, it is commonly known under the name of the “Devil.” A front view of the skull is shown in Fig. 35.

The prevailing colour of this animal is black, and the size about equal to that of an English Badger; its habits are fossorial, and it is very destructive to sheep. On account of the similarity in the number of its teeth this genus has been generally included in the next one, but in the structure of the teeth it is much nearer to _Thylacinus_. An extinct species is found in the Pleistocene deposits of the mainland of Australia.

It may be observed that the two premolars missing from the typical series of four in this and the next genus are the second and the fourth; the fourth milk-molar being likewise absent. In _Thylacinus_ and other Polyprotodonts with three premolars it is the second that is missing.

_Dasyurus._[44]—Dentition: _i_ ⁴⁄₃, _c_ ¹⁄₁, _p_ ²⁄₂, _m_ ⁴⁄₄; total 42. Upper incisors nearly equal, and placed vertically; first slightly longer, narrower, and separated from the rest. Lower incisors sloping forwards and upwards. Canines large and sharply pointed. Premolars with compressed and sharp-pointed crowns, and slightly developed anterior and posterior accessory basal cusps. True molars with numerous sharp-pointed cusps. In the upper jaw the first three with crowns having a triangular oral surface, the fourth small, simple, narrow, and placed transversely. In the lower jaw the molars more compressed, with longer cusps; the fourth not notably smaller than the others. Form viverrine. Ears long and narrow, prominent, and obtusely pointed. Hallux rudimentary, or absent; its metatarsal bone always present. Tail long and well clothed with hair. Humerus without an entepicondylar foramen. Vertebræ: C 7, D 13, L 6, S 2, C 18-20.

The Dasyures are small Civet-like animals with a gray or brown pellage profusely spotted with white; they are mostly inhabitants of the Australian continent and Tasmania, where in the economy of nature they take the place of the smaller predaceous Carnivora, the Cats, Civets, and Weasels of other parts of the world. They hide themselves in the daytime in holes among rocks or in hollow trees, but prowl about at night in search of the small living mammals and birds which constitute their prey. The species are not numerous, and include _D. maculatus_, about the size of a common Cat, inhabiting Tasmania and the southern part of Australia; _D. viverrinus_, Tasmania and Victoria; _D. geoffroyi_, nearly all Australia; _D. hallucatus_, North Australia; _D. albopunctatus_, New Guinea.

Remains referred to _D. viverrinus_ occur in the Australian Pleistocene deposits.

_Phascologale._[45]—This genus comprises a considerable number of small Marsupials, none of them exceeding a common Rat in size, differing from the Dasyures in possessing an additional premolar—the dentition being _i_ ⁴⁄₃, _c_ ¹⁄₁, _p_ ³⁄₃, _m_ ⁴⁄₄; total 46,—and having the teeth generally developed upon an insectivorous rather than a carnivorous pattern, the upper middle incisors being larger and inclined forwards, the canines relatively smaller, and the molars with broad crowns, armed with prickly tubercles. The muzzle is pointed. Ears moderately rounded and nearly naked. Feet broad and short. Fore feet with five subequal toes, having compressed, slightly curved, pointed claws. Hind feet with the four outer toes subequal, having claws similar to those in the fore feet; the hallux always distinct and partially opposable, though small and nailless. Tail long, very variable in its covering, being either bushy, crested, or nearly naked. Pouch represented merely by a few folds of skin. Mammæ varying from four to ten in number. The food of these animals is almost entirely insects; some species pursuing their prey among the branches of trees, while others are purely terrestrial. They are found throughout Australia, and also in New Guinea and the Aru and some of the adjacent islands.

_P. cristicaudata_, a species with a thick compressed tail ornamented upon its apical half with a crest of black hair, differs from the others by the very reduced size of the fourth premolar in the upper, and its complete absence in the lower jaw, thus forming an interesting transition in dentition towards _Dasyurus_. It constitutes the genus _Chætocercus_ of Krefft, but is included by Mr. O. Thomas in _Phascologale_, the frequent absence of the fourth lower premolar in _P. thorbeckiana_ indicating that the total absence of this tooth in the known specimens of this species cannot be regarded as of generic importance. All the members of this and the two following genera can be at once distinguished from _Dasyurus_ by the absence of white spots on the fur.

_Sminthopsis._[46]—The genus _Sminthopsis_ includes several small species allied to _Phascologale_ but characterised by the narrowness of the hind foot, and by the soles of the feet being either granulated or hairy, instead of naked.

_Antechinomys._[47]—The last genus of the _Dasyurinæ_ is _Antechinomys_, represented only by _A. laniger_ of Queensland and New South Wales. This elegant little mouse-like creature, which has large oval ears and a long tail with the terminal part bushy, is distinguished from _Sminthopsis_ by the absence of the hallux and the great elongation of the limbs. The tympanic bullæ of the skull are also unusually large, with the mastoid portion much swollen. A full account of the habits and anatomy of this animal, which appears to be of very rare occurrence, is given in the _Proc. Zool. Soc._ 1880, p. 454.

Subfamily =Myrmecobiinæ=.—Molars and premolars exceeding the normal number of seven on each side. Tongue, long cylindrical, and extensile.

[Illustration: FIG. 41.—_Myrmecobius fasciatus._ From Gould.]

_Myrmecobius._[48]—Dentition: _i_ ⁴⁄₃, _c_ ¹⁄₁, _p_ ³⁄₃, _m_ ⁵⁄₅ or ⁶⁄₆; total 52 or 56, being the largest number of teeth in any existing Marsupial. The distinction between the molars and premolars is founded not on a knowledge of the succession of the teeth, but on their form. The teeth are all small and (except the four posterior inferior molars) separated from each other by an interval. Head elongated, but broad behind. Muzzle long and pointed. Ears of moderate size, ovate, and rather pointed. Fore feet with five toes, all having strong, pointed, compressed claws, the second, third, and fourth nearly equal, the fifth somewhat, and the first considerably, shorter. Hind feet with no trace of hallux externally, but the metatarsal bone present. Tail long, clothed with long hairs. Fur rather harsh and bristly. Female without any pouch, the young when attached to the nipples being concealed only by the long hair of the abdomen. Vertebræ: C 7, D 13, L 6, S 3, C 23. A gland on the under surface of the body just in advance of the sternum.

Of this singular genus but one species is known, _M. fasciatus_ (Fig. 41), found in western and southern Australia. It is about the size of an English squirrel, to which animal its long bushy tail gives it some resemblance; but it lives entirely on the ground, especially in sterile, sandy districts, feeding on ants. Its prevailing colour is chestnut red, but the hinder part of the back is elegantly marked with broad, white, transverse bands on a dark ground.

The special interest of this form lies in its apparent relationship to those Mesozoic mammals which possess a large number of true molars (see p. 114); and it is suggested by Thomas that it may eventually be found advisable to include some of the latter in the present subfamily.

_Family_ PERAMELIDÆ.

Dentition: _i_ ⁴⁻⁵⁄₃, _c_ ¹⁄₁, _p_ ³⁄₃, _m_ ⁴⁄₄; total 46 or 48. Upper incisors small, with short broad crowns. Lower incisors moderate, narrow, proclivous. Canines well developed. Premolars compressed, pointed. Molars with quadrate tuberculated crowns. Fourth premolar preceded by a small molariform tooth, which remains in place until the animal is nearly full grown. Fore feet with two or three of the middle toes of nearly equal size, and provided with strong, sharp, slightly curved claws; the other toes rudimentary. Hind feet long and narrow; the hallux rudimentary or absent; the second and third toes very slender, and united in a common integument; the fourth very large, with a stout elongated conical claw; the fifth smaller than the fourth (see Fig. 43). The ungual phalanges of the large toes of both feet cleft at their extremities (as in _Manis_ among the Edentata, but in no other Marsupials). Head elongated. Muzzle long, narrow, and pointed. Stomach simple. Cæcum of moderate size. Pouch complete, opening backwards. Alone among Marsupials they have no clavicles.

The _Peramelidæ_ form a very distinct family, in some respects intermediate between the sarcophagous _Dasyuridæ_ and the phytophagous _Macropodidæ_. In dentition they resemble the former, but they agree with the latter in the peculiar structure of the hind feet. In the construction of the fore feet they differ from all other Marsupials.

The Bandicoots, as these Marsupials are popularly termed, are of fossorial habits, and subsist either on an insectivorous or omnivorous diet. It has been generally considered that their syndactylous feet indicate direct affinity with the Diprotodonts, but owing to the essentially Polyprotodont character of the organisation—which extends even to their carpal and tarsal bones—Thomas dissents from this view, and concludes that their syndactylism is an independently acquired character, and that they are really a direct offshoot from the _Dasyuridæ_. Some individuals are remarkable for the presence of a longitudinal groove in the root of the canines, by which feature they approximate to some of the Mesozoic Polyprotodont forms. They may be divided into three genera.

[Illustration: FIG. 42.—_Perameles gunni._ From Gould.]

_Perameles._[49]—Anterior and posterior extremities not differing greatly in development. Fore feet with the three middle toes well developed, the third slightly larger than the second, the fourth somewhat shorter, provided with long, strong, slightly curved, pointed claws. First and fifth toes very short and without claws. Hind feet with hallux of one or two phalanges, forming a distinct tubercle visible externally; the second and third toes very slender, of equal length, joined as far as the ungual phalanges, but with distinct claws; the fifth intermediate in length between these and the largely developed fourth toe. Ears of moderate or small size, ovate, pointed. Tail rather short, clothed with short adpressed hairs. Fur short and harsh. Vertebræ; C 7, D 13, L 6, S 1, C 17. Skull long and narrow, with the bulla single, and its mastoid portion not inflated.

The animals of this genus are all small, and live entirely on the ground, making nests composed of dried leaves, grass, and sticks in hollow places. They are rather mixed feeders; but insects, worms, roots, and bulbs constitute their ordinary diet. The various species are widely distributed over Australia, Tasmania, New Guinea, and several of the adjacent islands, as Aru, Kei, and New Ireland. The best known are—_P. gunni_ (Fig. 42), _bougainvillei_, _nasuta_, _obesula_, and _macrura_ from Australia, and _P. doreyana_, _raffrayana_, and _longicaudata_ from New Guinea.

Remains apparently referable to existing species are found in the cave-deposits of New South Wales.

_Peragale._[50]—Molar teeth curved, typically with longer crowns and shorter roots than in the last. Hinder extremities proportionally longer, and hallux without claw. Muzzle much elongated and narrow. Fur soft and silky. Ears very large, long, and pointed. Tail long, its apical half clothed on the dorsal surface with long hairs which form a crest. Vertebræ: C 7, D 13, L 6, S 2, C 23. Skull distinguished from that of _Perameles_ by the large size and double structure of the auditory bulla, of which the mastoid portion is inflated. There is also an abrupt contraction of the muzzle at the third premolar.

The type species of Rabbit-Bandicoot (_P. lagotis_), as these animals are called, is found in Western Australia, and also occurs fossil in the cave-deposits of New South Wales. It is the largest member of the family, being about the size of the common Rabbit, to which animal it bears sufficient superficial resemblance to have acquired the name of “Native Rabbit” from the colonists. It burrows in the ground, but in other respects resembles the true Bandicoots in its habits.

The smaller _P. leucura_ has short-crowned molars, with distinct cusps, which are almost obsolete in the type species.

[Illustration: FIG. 43.—Skeleton of right hind foot of _Chœropus castanotis_. _c_, Calcaneum; _a_, astragalus; _cb_, cuboid; _n_, navicular; _c³_, ectocuneiform; II and III, the conjoined second and third digits; IV, the large and only functional digit; V, the rudimentary fifth digit.]

_Chœropus._[51]—Dentition generally resembling that of _Perameles_, but the canines are less developed, and in the upper jaw two-rooted. Limbs very slender; posterior nearly twice the length of the anterior. Fore feet with the functional toes reduced to two, the second and third, of equal length, with closely united metacarpals and short, sharp, slightly curved, compressed claws. First toe represented by a minute rudiment of a metacarpal bone; the fourth by a metacarpal and two small phalanges without a claw, and not reaching the middle of the metacarpal of the third; fifth entirely absent. Hind foot (Fig. 43) long and narrow, mainly composed of the strongly developed fourth toe, terminating in a conical pointed nail, with a strong pad behind it; the hallux absent or represented by a rudimentary metatarsal; the remaining toes completely developed, and with claws, but exceedingly slender; the united second and third reaching a little way beyond the metatarso-phalangeal articulation of the fourth; the fifth somewhat shorter. Tail not quite so long as the body, and covered with short hairs forming a slight crest. Ears large and pointed, and folded down when the animal is at rest. Fur soft and loose. Vertebræ: C 7, D 13, L 6, S 1, C 20. Skull short and wide, with a small and single bulla, and a contraction of the muzzle at the third premolar.

The only known species of this genus (Fig. 44), chiefly remarkable for the singular construction of its limbs, is an animal about the size of a small Rat, found in the interior of the Australian continent. Its general habits and food appear to resemble those of the other _Peramelidæ_. It was first described as _C. ecaudatus_ by Ogilby from a mutilated specimen, but the specific name was afterwards changed, as being inappropriate, by Gray to _castanotis_.

_Suborder_ DIPROTODONTIA.

For the leading characters of this group, see page 132.

_Family_ PHASCOLOMYIDÆ.

Dentition: _c_ ¹⁄₁, _i_ ⁰⁄₀, _p_ ¹⁄₁, _m_ ⁴⁄₄ = 24. All the teeth with persistent pulps. The incisors large, scalpriform, with enamel only on the front surface, as in the Rodentia. The molars strongly curved, forming from the base to the summit about a quarter of a circle, the concavity being directed outwards in the upper and inwards in the lower teeth. The first of the series, or premolar, appears to have no milk-predecessor, and is single-lobed; the other four composed of two lobes, each subtriangular in section. Limbs equal, stout, and short. Fore feet with five distinct toes, each furnished with a long, strong, and slightly curved nail, the first and fifth considerably shorter than the other three. Hind feet with a very short nailless hallux, the second, third, and fourth toes partially united by integument, of nearly equal length, the fifth distinct and rather shorter; all four provided with long and curved nails. In the skeleton of the foot, the second and third toes are distinctly more slender than the fourth, showing a slight tendency towards the peculiar character so marked in the next two families. Tail rudimentary. Stomach simple, provided with a special gland situated near the cardiac orifice. Cæcum very short, wide, and with a peculiar vermiform appendage. Pouch present. The auditory bullæ of the skull are imperfect, open behind, with their anterior wall formed by a descending process of the squamosal, instead of the alisphenoid. Masseteric fossa of mandible with a perforation and a deep pit.

[Illustration: FIG. 44.—_Chœropus castanotis._ From Gould.]

_Phascolomys._[52]—The existing Wombats (Fig. 45) comprise three species, all of which are included in the one genus _Phascolomys_, and all of which date from the Pleistocene.

In the typical group we find the following characters. Fur rough and coarse. Ears short and rounded. Muffle naked. Postorbital process of the frontal bone obsolete. Ribs fifteen pairs. Vertebræ: C 7, D 15, L 4, S 4, C 10-12. The Wombat of Tasmania and the islands of Bass’s Straits (_P. ursinus_) and the closely similar but larger animal of the southern portion of the mainland of Australia (_P. mitchelli_) belong to this group.

[Illustration: FIG. 45.—Common Wombat (_Phascolomys ursinus_).]

In the second group the characters are as follows. Fur smooth and silky. Ears large and more pointed. Muffle hairy. Frontal region of skull broader than in the other group, with well-marked postorbital processes. Ribs thirteen. Vertebræ: C 7, D 13, L 6, S 4, C 15-16. One species, _P. latifrons_, the Hairy-nosed Wombat of Southern Australia.

In their general form and actions the Wombats resemble small bears, having a somewhat similar shuffling manner of walking, but they are still shorter in the legs, and have broader, flatter backs than bears. They live entirely on the ground, or in burrows or holes among rocks, never climbing trees, and feed entirely on grass, roots, and other vegetable substances. They sleep during the day, and wander forth at night in search of food, and are shy and gentle in their habits generally, though they can bite strongly when provoked. The only noise the common wombat makes is a low kind of hissing, but the Hairy-nosed Wombat is said to emit a short quick grunt when annoyed. The prevailing colour of the last-named species, as well as of _P. ursinus_ of Tasmania, is a brownish gray. The large wombat of the mainland is very variable in colour, some individuals being found of a pale yellowish brown, others dark gray, and some quite black. The length of head and body is about three feet.

It is noteworthy that _P. mitchelli_ was first described from the evidence of fossil remains, the living form subsequently described as _P. platyrhinus_ being found to be indistinguishable. Other extinct species occur in the Pleistocene of Australia.

_Phascolonus._[53]—Remains of a large extinct Wombat, which must have nearly equalled the dimensions of a Tapir, occur in the Pleistocene of Queensland, and have been described as _Phascolonus_. It is probable that the expanded and flattened upper incisors from the same deposits upon the evidence of which the presumed genus _Sceparnodon_ was founded, are likewise referable to the same form. The characters of both the upper and lower incisors distinguish _Phascolonus_ from _Phascolomys_.

_Family_ PHALANGERIDÆ.

Dentition extremely variable, owing to the presence of minute rudimental teeth not constant in the same species, or even in the two sides of the jaws of the same individual; exclusive, however, of _Tarsipes_, the formula _i_ ³⁄₁, _c_ ¹⁄₀, _p_ ²⁻³⁄₀₋₂, _m_ ³⁻⁴⁄₃₋₄ represents fairly the general condition of the functional teeth. First incisors long and stout; the lower pair very large and pointed, but without the scissor-like action found in the existing _Macropodidæ_; second and third lower incisors minute and probably functionless. Fourth premolar generally secant; milk-molar generally minute and deciduous at an early period. Molars either with sharp cutting-crests or bluntly tuberculate; fourth sometimes absent. Mandible without pit, and at most a very minute perforation in the masseteric fossa. Limbs subequal. Fore feet with five distinct, subequal toes, furnished with claws. Hind feet short and broad, with five well developed toes; the hallux large, nailless and opposable; the second and third slender, and united by a common integument as far as the claws. Tail generally long, and frequently more or less prehensile. Stomach simple. Cæcum present (except in _Tarsipes_), and usually large. Pouch complete. Animals of small or moderate size and arboreal habits, usually feeding on a vegetable or mixed diet, inhabiting Australia and the Papuan Islands.

The homologies of the lower functionless teeth between the first incisor and fourth premolar are very difficult to determine, but it is probable that one represents a canine only when the largest known number is present; this tooth, according to Mr. Thomas, being the first to disappear.

Phalangers are small woolly-coated animals, with long, powerful, and often prehensile tails, large claws, and, as in the American opossums, with opposable nailless great toes. Their expression seems in the day to be dull and sleepy, but by night they appear to decidedly greater advantage. They live mostly upon fruit, leaves, and blossoms, although some few feed habitually upon insects, and all relish, when in confinement, an occasional bird or other small animal. Several of the Phalangers possess flying membranes stretched between their fore and hind limbs (Fig. 48), by the help of which they can make long and sustained leaps through the air, like the Flying Squirrels, but it is interesting to notice that the possession of these flying membranes does not seem to be any indication of special affinity, the characters of the skull and teeth sharply dividing the flying forms, and uniting them with other species of the non-flying groups. Their skulls (Fig. 47) are as a rule broad and flattened, with the posterior part swollen out laterally, owing to the numerous air-cells situated in the substance of the squamosal.

The Phalangers are interesting from an historical point of view, since the Gray Cuscus (_Phalanger orientalis_) was the first of the Marsupials of the eastern hemisphere brought to the notice of Europeans, having been described in a work published at Leyden in 1611, from an account of a specimen seen at Amboyna during the third expedition of Admiral Van der Hagen.

The present family corresponds to the _Dasyuridæ_ among the Polyprotodonts as presenting, on the whole, the most generalised types of the suborder. The existing forms may be divided into three subfamilies.

Subfamily =Tarsipedinæ=.—Cheek-teeth almost rudimentary and variable in number. Tongue long, slender, pointed, and very extensile. Tail long. Cæcum absent.

[Illustration: FIG. 46.—_Tarsipes rostratus._ From Gould.]

_Tarsipes._[54]—So named from some supposed resemblance of its foot to that of the Lemurine genus _Tarsius_; but it must be remarked that it has none of the peculiar elongation of the calcaneum and navicular so characteristic of that genus. Head with elongated and slender muzzle. Mouth-opening small. The two lower incisors are long, very slender, sharp-pointed, and horizontally placed. All the other teeth are simple, conical, minute, and placed at considerable and irregular intervals apart in the jaws, the number appearing to vary in different individuals and even on different sides of the same individual. The formula, in a specimen in the Museum of the Royal College of Surgeons, is _i_ ²⁄₁, _c_ ¹⁄₀, _p_ and _m_ ³⁄₂ on one side, and ⁴⁄₃ on the other; total 20. Rami of the mandible extremely slender, nearly straight, and without coronoid process or inflected angle. Fore feet with five well-developed toes, furnished with small, flat, scale-like nails, not reaching to the extremity of the digits. Hind feet rather long and slender compared with those of the _Phalangerinæ_, having a well-developed opposable and nailless hallux; second and third digits syndactylous, with sharp compressed curved claws; the fourth and fifth free, and with small flat nails. Ears of moderate size and rounded. Tail longer than the body and head, scantily clothed with short hairs, prehensile. Vertebræ: C 7, D 13, L 5, S 3, C 24.

Of this singular genus but one species, _T. rostratus_ (Fig. 46), is known, about the size of a common Mouse. It inhabits Western Australia, lives in trees and bushes, uses its tail in climbing, and feeds on honey, which it procures by inserting its long tongue into the blossoms of _Melaleucæ_, etc. One kept in confinement by Mr. Gould was also observed to eat flies.

Subfamily =Phalangerinæ=.—Teeth normal. One or more rudimentary teeth between the upper canine and fourth premolar, and between the first lower incisor and fourth premolar. Tongue of ordinary structure. No cheek-pouches. Stomach and ascending colon simple. Cæcum long, simple. Tail well-developed, generally prehensile.

A numerous group of animals, varying from the size of a mouse to that of a large cat, arboreal in their habits, and abundantly distributed throughout the Australian region. The members of this group are the typical representatives of the family, and are commonly known to the colonists as Opossums.

_Phalanger._[55]—The typical genus _Phalanger_ (_Cuscus_) presents the following characters. No flying membrane; size large or medium, and build stout and clumsy; fur thick and woolly. Ears short or medium, hairy externally, and in some cases also internally. Toes of fore feet subequal, their relative lengths in the order 4, 3, 5, 2, 1. Claws long, stout, and curved. Soles of feet naked and striated, with large ill-defined pads. Tail stout and markedly prehensile, with the proximal half furred like the body, and the terminal portion entirely naked. Four mammæ. Skull (Fig. 47) stout and strong, with large vacuities in the hinder half of the palate, and the auditory bullæ thick and inflated. Dentition usually _i_ ³⁄₂, _c_ ¹⁄₀, _p_ ³⁄₃, _m_ ⁴⁄₄. First upper incisor with nearly circular section, or only slightly flattened in front; canine more or less closely approximated to third incisor (which is very small), and situated partly in front of the suture between the premaxilla and maxilla. Fourth premolar large, secant, and placed obliquely to line of molars. Molars four-cusped, with the inner cusps of the upper ones crescentoid, and imperfect transverse ridges connecting each pair of cusps.

[Illustration: FIG. 47.—Left lateral view of skull of Gray Cuscus (_Phalanger orientalis_). After Peters.]

The Cuscuses are curious sleepy-looking animals, inhabiting the various islands of the East Indian Archipelago as far west as Celebes, and being the only Marsupials found west of New Guinea. As already noted, it was a member of this genus, the Gray Cuscus (_P. orientalis_), a native of Amboyna, Timor, and the neighbouring islands, which was the first Australasian Marsupial known to European naturalists. There are altogether five species known, all of about the size of a large cat; their habits resemble those of other Phalangers, except that they are said to be somewhat more carnivorous.

_Trichosurus._[56]—The members of the genus _Trichosurus_ are of relatively large size, and are distinguished from _Phalanger_ by the following characters. Ears more or less hairy behind. Relative lengths of toes of fore feet in the order 4, 3, 2, 5, 1. Hair on the soles of the hind feet beneath the heel, but not elsewhere. Tail thick, not tapering, covered with bushy hair up to the extreme tip, which is naked, but with a naked strip on the inferior surface in the distal third or half. A gland on the chest. Dentition usually _i_ ³⁄₂, _c_ ¹⁄₀, _p_ ²⁄₂, _m_ ⁴⁄₄. Upper incisors of nearly uniform length, the first much flattened in front. Canine situated some distance behind the third upper incisor, which it scarcely exceeds in size. Last premolar and molars very similar to those of _Phalanger_.

The true Phalangers comprise two species, of which the best known is the Vulpine Phalanger (_T. vulpecula_), so common in zoological gardens, where, however, it is seldom seen, owing to its nocturnal habits. It is of about the size and general build of a small fox, whence its name. In the typical variety the colour is gray, with a yellowish white belly, white ears, and a black tail. This variety is a native of the greater part of the continent of Australia, but is replaced in Tasmania by the closely allied Brown Phalanger (_var. fuliginosa_). Its habits are very similar to those of the Yellow-bellied Flying-Phalanger (_Petaurus australis_) described below, except that it is unable to take the flying leaps of that animal. Like all the other phalangers, its flesh is freely eaten both by the natives and the lower class of settlers.

_Pseudochirus._[57]—The genus _Pseudochirus_ agrees with the preceding in the absence of a flying membrane, and presents the following leading characters. Size large or medium. Fur comparatively short and woolly. Ears medium or short, hairy behind, although seldom closely furred over all this aspect. Claws medium. Fore toes subequal, the first two distinctly opposable to the other three. Soles of feet naked, with large, striated, round pads, and hair beneath the heels. Tail tapering, markedly prehensile, with its distal third and the whole of the under surface short-haired; tip naked underneath for a short distance. Four mammæ. No gland on chest. Skull with larger nasals than in the preceding genera; the posterior part of the palate in most cases fully ossified, and the auditory bullæ generally somewhat inflated. Dentition (at most) _i_ ²⁻³⁄₂, _c_ ⁰⁻¹⁄₀, _p_ ³⁄₃, _m_ ⁴⁄₄. Upper teeth nearly uniform in length, but the first incisor distinctly longer than second. Upper premolars variable. Molars with both inner and outer cusps distinctly crescentoid, and recalling those of the Selenodont Artiodactyle Ungulates.

_Range._—Tasmania, Australia, and New Guinea.

There are about ten species of this genus known, of which the commonest is Cook’s Ring-tailed Phalanger (_Pseudochirus peregrinus_), an animal discovered by Captain Cook during his first voyage, at Endeavour river, North Queensland.

The complex and sub-selenodont character of the molars of this and the following genus readily distinguish them from the more typical Phalangers, and show an approximation to the type of dentition prevailing in _Phascolarctus_; according, however, to Mr. O. Thomas, a tendency towards the same structure is observable in unworn molars of young Cuscuses. The genus may be divided into three groups, of which the first, as typified by the common _P. peregrinus_, is restricted to Australia and Tasmania, while the third, as represented by _P. canescens_, is only found in New Guinea. _P. albertisi_ may be taken as the type of the second group, which is represented by that species in New Guinea, and by _P. archeri_ in Queensland. With the exception of _P. peregrinus_, the species have a more or less restricted range. Remains of _Pseudochirus_, probably referable to existing species, are found in the cave-deposits of New South Wales.

_Petauroides._[58]—With the genus _Petauroides_, containing only the single species _P. volans_, we come to the first of the Flying-Phalangers, characterised by the possession of a living membrane along the flanks. The characters of this genus are as follows. Size large. Fur very long and silky. Ears large and oval, thickly furred on the back, but naked internally. Flying-membrane reaching from wrist to ankle, but very narrow along the sides of the forearm and lower leg. Fore toes subequal, their relative lengths in the order 4, 3, 5, 2, 1. Claws long, curved, and sharp. Tail long, cylindrical, and bushy, except near its tip, where it is naked and prehensile. Skull short and broad, with the nasals short, and not extending nearly as far forwards as the premaxillæ. Large vacuities in hinder part of palate. Auditory bullæ inflated and smooth. Dentition usually _i_ ³⁄₂, _c_ ¹⁄₀, _p_ ²⁄₂, _m_ ⁴⁄₄. General characters of teeth very similar to those of _Pseudochirus_, but the first upper incisor scarcely longer than the second.

The single species is found in Australia, from Queensland to Victoria, and is commonly known as the Taguan Flying-Phalanger. The structure of the skull and teeth indicates close affinity with _Pseudochirus_, although the external form is widely different in the two genera. This Phalanger seems, indeed, to be, so to speak, a very specialised _Pseudochirus_, in which the teeth have become somewhat further diminished and the flying membrane has been developed.

_Dactylopsila._[59]—The genus _Dactylopsila_ is one of the forms without any trace of a flying membrane, its characters being as follows. Size medium. Body striped black and white. Ears oval, nearly naked at the ends. Fore toes of very unequal length, the fourth being enormously elongated; fourth and fifth toes of pes also markedly elongated. Claws long, moderately curved. Tail long, cylindrical, and evenly bushy, with the extremity more or less naked below. Skull narrow, but with the zygomatic arches greatly expanded; palate fully ossified. Dentition: _i_ ³⁄₃, _c_ ¹⁄₀, _p_ ³⁄₂, _m_ ⁴⁄₄. Upper incisors very large, the third being directed horizontally forwards; canine small and approximated to the third incisor, which it resembles. The fourth premolar of moderate size, with its longer axis placed obliquely. First lower incisor longer than in any other genus. Molars oblong, with four cusps.

The typical _D. trivirgata_, or Striped Phalanger, inhabits the Papuan and North Australian sub-region; a second species (_D. palpator_), characterised by the still greater elongation of the fourth finger, occurring in South New Guinea. These animals are said to be of insectivorous habits, the elongated fourth finger, as in the analogous instance of the Lemuroid genus _Chiromys_, being apparently specially adapted for extracting insects and larvæ from their hiding places.

_Petaurus._[60]—Size medium or small. Fur very soft and silky. A broad flying membrane extending from the outer side of the fifth digit of the manus to the ankle. Fore toes usually increasing regularly in length from the first to the fifth, but in some of the smaller species the fourth is the longest. Claws strong, sharp, and much curved. Tail long, evenly bushy to the extremity. Glands on the chest and between the ears. Skull short and wide, with the nasals expanded posteriorly, and usually two small palatal vacuities near the second molars. Auditory bullæ inflated, and variable in size. Dentition: _i_ ³⁄₂, _c_ ¹⁄₀, _p_ ³⁄₃, _m_ ⁴⁄₄. First upper incisors very large, and taller than canine. Molars with square crowns rounded at the angles, and four cusps, except in the last, which is triangular.

This genus, which ranges from New Ireland to South Australia, but is not found in Tasmania, contains three species, the largest of which is the Yellow-bellied Flying-Phalanger (_P. australis_), whose habits are recorded by Mr. Gould as follows. “This animal is common in all the brushes of New South Wales, particularly those which stretch along the coast from Port Philip to Moreton Bay. In these vast forests trees of one kind or another are perpetually flowering, and thus offer a never-failing supply of the blossoms upon which it feeds; the flowers of the various kinds of gums, some of which are of great magnitude, are the principal favourites. Like the rest of the genus, it is nocturnal in its habits, dwelling in holes and in the spouts of the larger branches during the day, and displaying the greatest activity at night while running over the small leafy branches, frequently even to their very extremities, in search of insects and the honey of the newly-opened blossoms. Its structure being ill adapted for terrestrial habits, it seldom descends to the ground except for the purpose of passing to a tree too distant to be reached by flight. When chased, or forced to flight it ascends to the highest branch and performs the most enormous leaps, sweeping from tree to tree with wonderful address; a slight elevation gives its body an impetus which, with the expansion of its membrane, enables it to pass to a considerable distance, always ascending a little at the extremity of the leap; by this ascent the animal is prevented from receiving the shock which it would otherwise sustain.”

A second species, _P. sciureus_, in some ways one of the most beautiful of all mammals, has been chosen for the accompanying woodcut.

_Gymnobelideus._[61]—Like _Petaurus_ in every respect, but without any trace of a flying membrane, and with the fifth digit of the manus slightly shorter than the third. This genus is represented only by _G. leadbeateri_ of Victoria, and according to Mr. Thomas, may be regarded as the primitive form from which the specialised _Petaurus_ has been developed.

[Illustration: FIG. 48.—Squirrel Flying-Phalanger (_Petaurus sciureus_).]

_Dromicia._[62]—Size small, and general appearance dormouse-like. Ears large and thin, almost naked, and without internal or basal tufts. No flying membrane. Digits of normal proportions, the relative lengths of those of the manus in the order 3, 4, 2, 5, 1; fore claws rudimentary, hind ones long and sharp. Tail mouse-like, cylindrical, furry at base, the remainder scaly, with fine hairs, except at the tip, which is naked and prehensile. Skull short and broad, with the hinder part of the palate incomplete, and the auditory bullæ large, much inflated, and transparent. Dentition: _i_ ³⁄₂, _c_ ¹⁄₀, _p_ ³⁄₃, _m_ ³⁻⁴⁄₃₋₄. First upper incisor spatulate, and much longer than either of the others. Canine large, placed at some distance behind the third incisor. Molars (except the last) with evenly rounded crowns, carrying four small smooth cusps.

This genus, which occurs in New Guinea, Western Australia, and Tasmania, is represented by four species. It seems to be intermediate between _Petaurus_ and _Acrobates_, and it has apparently had to yield place to those more highly organised types in regions where they have come in contact with one another.

_Distœchurus._[63]—Size small. Ears rather short, thinly covered with hair, but with small tufts at the base. No flying membrane. Digits of normal proportions, without expanded terminal pads. Claws curved and sharp. Tail, skull, and dentition as in _Acrobates_, with the exception that the fourth premolar is small in the upper, and absent in the lower jaw.

The one species of Feather-tailed Phalanger (_D. pennatus_) is found in New Guinea.

_Acrobates._[64]—Size very small. Ears moderate, thinly covered with hair, but with small tufts round the base and on the internal prominences. A narrow flying membrane, fringed with long hairs, running from the elbow to the flank, and from the latter to the knee. Four mammæ. Digits furnished with expanded and striated terminal pads, the relative length of those of the manus being in the order 4, 3, 5, 2, 1. Claws sharp, although somewhat concealed by the terminal pads. Tail short-haired above and below, with a broad fringe on either side. Skull short, wide, and depressed. Posterior portion of palate very imperfectly ossified; anterior palatal vacuities almost confined to the maxillæ. Auditory bullæ low, rounded, and but slightly prominent. Dentition: _i_ ³⁄₂, _c_ ¹⁄₀, _p_ ³⁄₃, _m_ ³⁄₃. Teeth sharp, and of an insectivorous type. Upper canine long, and approximated to third incisor. The three upper premolars large, functional, and taller than the molars. Molars small and rounded, with smooth unridged cusps.

There is only one species in this genus, the beautiful little Pigmy Flying-Phalanger (_A. pygmæus_), not so big as a Mouse, which is found in Queensland, New South Wales, and Victoria, and feeds on the honey it abstracts from flowers, and on insects. Its agility and powers of leaping are exceedingly great, and it is said by Mr. Gould to make a most charming little pet.

Subfamily =Phascolarctinæ=.—Teeth large, normal; no rudimentary premolars before the last upper premolar, or any teeth between the first lower incisor and fourth premolar. Tongue of ordinary structure. Distinct cheek-pouches. Stomach with a special gland near the cardiac orifice. Cæcum very long, and (with the upper portion of the colon) dilated and provided with numerous longitudinal folds of mucous membrane. In many anatomical characters, especially the possession of a special gastric gland, this group resembles the _Phascolomyidæ_.[65]

[Illustration: FIG. 49.—Skeleton of right hind foot of Koala (_Phascolarctus cinereus_), showing the stout opposable hallux, followed by two slender toes, which in the living animal are enclosed as far as the nails in a common integument.]

_Phascolarctus._[66]—Dentition: _i_ ³⁄₁, _c_ ¹⁄₀, _p_ ¹⁄₁, _m_ ⁴⁄₄; total 30. Upper incisors crowded together, cylindroidal, the first much larger than the others, with a bevelled cutting edge (Fig. 36). Canine very small; a considerable interval between it and the premolar, which is as long from before backwards but not so broad as the true molars, and has a cutting edge, with a smaller parallel inner ridge. The molars slightly diminishing in size from the first to the fourth, with square crowns, each bearing four pyramidal cusps, with curved ridges radiating from them, and having a structure very similar to these of _Pseudochirus_. The lower incisors are semiproclivous, compressed and tapering, bevelled at the ends. Premolars and molars in continuous series, as in the upper jaw. Milk-tooth very minute, and almost functionless. Fore feet with the two inner toes slightly separated from and opposable to the remaining three, all with strong, curved, and much compressed claws. Hind foot (Fig. 49) with the hallux placed very far back, large and broad, the second and third (united) toes considerably smaller than the other two; the fourth the largest. No external tail. Fur dense and woolly. Ears of moderate size, thickly clothed with long hairs. Vertebræ: C 7, D 11, L 8, S 2, C 8. Ribs eleven pairs, a rare exception to the usual number (13) in the Marsupialia.

There is but one species, the Koala or Native Bear of the Australian colonists (_P. cinereus_), an animal of comparatively large size and heavy build (Fig. 50), found in the south-eastern parts of the Australian continent. It is about two feet in length, and of an ash-gray colour, an excellent climber, and residing generally in lofty _Eucalyptus_ trees, on the buds and tender shoots of which it feeds, though occasionally descending to the ground in the night.

EXTINCT PHALANGEROIDS.

Numerous imperfect remains recently described by De Vis are regarded as indicating large extinct types of _Phalangeridæ_, but further evidence is required before all these determinations can be definitely accepted. Thus part of an upper jaw is provisionally referred to a large species of _Pseudochirus_, while part of a scapula is made the type of a genus _Archizonurus_ which appears to be allied to the former. Another fragmentary scapula is considered to indicate a large _Phalanger_. Finally, part of a fibula, described under the name of _Koalemus_ is regarded as affording evidence of the former existence of a large ancestral form allied to the Koala, and it is suggested that an upper jaw with teeth may belong to the same or an allied type.

[Illustration: FIG. 50.—The Koala (_Phascolarctus cinereus_). From Sclater, _Proc. Zool. Soc._ 1880, p. 355.]

_Thylacoleo._[67]—Dentition of adult: _i_ ³⁄₁, _c_ ¹⁄₀, _p_ ³⁄₃, _m_ ¹⁄₂; total 28. First upper incisor much larger than the others; canine and first two premolars rudimentary. In the lower jaw the two small anterior premolars are functionless, and often deciduous; posterior premolars of both jaws formed on the same type as those of _Potorous_, but relatively much larger; true molars rudimentary, tubercular. One species, _T. carnifex_. This animal presents a most anomalous condition of dentition, the functional teeth being reduced to one pair of large cutting incisors situated close to the median line, and one great, trenchant, compressed premolar, on each side above and below. It was first described as a carnivorous Marsupial, and named, in accordance with its presumed habits, “as one of the fellest and most destructive of predatory beasts”; but, as its affinities are certainly with the _Phalangeridæ_ and _Macropodidæ_, and its dentition completely unlike that of any known predaceous animal, this view has been called in question.

[Illustration: FIG. 51.—Front view of skull of _Thylacoleo carnifex_, restored. ¹⁄₃ natural size. From _Quart. Journ. Geol. Soc._ vol. xxiv. p. 312.]

The dentition is nearer to that of the existing _Phalangeridæ_ than to that of the _Macropodidæ_, and the genus may be provisionally regarded as the type of a distinct subfamily of the former.

_Family_ MACROPODIDÆ.

Dentition _i_ ³⁄₁, _c_ ⁰⁻¹⁄₀, _p_ ²⁄₂, _m_ ⁴⁄₄. Incisors sharp and cutting, those of the lower jaw frequently having a scissor-like action against one another; upper canine, if present, small. Penultimate premolar shed with the fourth milk-molar, which is molariform and long persistent. Molars wide, and either transversely ridged or bluntly tuberculate. Premolars and molars moving forwards in the skull as the age of the animal increases, this being most marked in the larger species. Masseteric fossa of mandible hollowed out below into a deep cavity walled in externally by a plate of bone, and communicating with the inferior dental canal by a large foramen. Hind limbs usually larger than the anterior ones, and progression generally saltatorial. Fore feet with five digits; hind feet syndactylous, the fourth digit being very large and strongly clawed; hallux usually absent. Tail generally long and hairy, occasionally prehensile; stomach sacculated. Pouch large and opening forwards.

[Illustration: FIG. 52.—Skeleton of right hind foot of Kangaroo.]

The _Macropodidæ_ or Kangaroos, taken as a whole, form a very well-marked family, easily distinguished from the other members of the suborder by their general conformation, and by peculiarities in the structure of their limbs, teeth, and other organs. They vary in size from that of a sheep down to a small rabbit. The head, especially in the larger species, is small, compared with the rest of the body, and tapers forward to the muzzle. The shoulders and fore limbs are feebly developed, and the hind limbs usually of disproportionate strength and magnitude, which gives them a peculiarly awkward appearance when moving about on all fours, as they occasionally do when feeding. Rapid progression is, however, performed only by the powerful hind limbs, the animal covering the ground by a series of immense bounds, during which the fore part of the body is inclined forwards, and balanced by the long, strong, and tapering tail, which is carried horizontally backwards. When not moving they often assume a perfectly upright position, the tail aiding the two hind legs to form a sort of supporting tripod, and the front limbs dangling by the side of the chest. This position gives full scope for the senses of sight, hearing, and smell to warn of the approach of enemies, from which these animals save themselves by their bounding flight. The fore paws have live distinct digits, each armed with a strong curved claw.

The hind foot (Fig. 52), as being a typical example of the syndactylous modification, may be noticed in some detail. It is extremely long and narrow, and (with only one exception) without any hallux or great toe. It consists mainly of one very large and strong toe, corresponding to the fourth of the human or other typically developed foot, ending in a strong, curved, and pointed claw. Close to the outer side of this lies a smaller fifth digit, and to the inner side two excessively slender toes (the second and third), bound together almost to the extremity in a common integument. The two little claws of these toes, projecting together from the skin, may be of use in scratching and cleaning the fur of the animal, but the toes themselves must have quite lost all connexion with the functions of support or progression.

The dentition of the Kangaroos, functionally considered, consists of sharp-edged incisors, most fully developed near the median line of the mouth, for the purpose of cropping the various kinds of herbage on which they feed, and ridged and tuberculated molars for crushing it, there being no tusks or canines for offensive or defensive purposes.

The number of vertebræ is—in the cervical region 7, dorsal 13, lumbar 6, sacral 2, caudal varying according to the length of the tail, but generally from 21 to 25. In the fore limb the clavicle and the radius and ulna are well developed, allowing of considerable freedom of motion of the hand. The pelvis has large epipubic or “marsupial” bones. The femur is short, and the tibia and fibula are of great length, as is the foot, the whole of which is applied to the ground when the animal is at rest in the upright position.

[Illustration: FIG. 53.—The Great Gray Kangaroo (_Macropus giganteus_).]

The stomach is of large size, and very complex, its walls being puckered up by longitudinal muscular bands into a great number of sacculi, like those of the human colon. The alimentary canal is long, and the cæcum well developed. All the species have a marsupium or pouch formed by a fold of the skin of the abdomen, covering the mammary glands with their four nipples. In this pouch the young are placed as soon as they are born; there their growth and development proceeds; and to it they resort temporarily for the purpose of shelter, concealment, or transport, for some time after they are able to run and jump about the ground and feed upon the same herbage which forms the nourishment of the parent. During the early period of their sojourn in the pouch, the blind, naked, helpless young creatures (which in the Great Kangaroo [Fig. 53] scarcely exceed an inch in length) are attached by their mouths to the nipples of the mother, and are fed by milk injected into their stomach by the contraction of the muscle covering the mammary gland.

The Kangaroos are all vegetable feeders, browsing on grass and various kinds of herbage, the smaller species also eating roots. They are naturally timid, inoffensive creatures; but the larger ones when hard pressed will turn and defend themselves, sometimes killing a dog by grasping it in their fore paws, and inflicting terrible wounds with the sharp claws of their powerful hind legs, sustaining themselves meanwhile upon the tail. A few aberrant forms are arboreal. The great majority are inhabitants of Australia and Tasmania, forming one of the most prominent and characteristic features of the fauna of these lands, and in the scenery of the country, as well as the economy of nature, performing the part of the deer and antelopes of other parts of the world, which are entirely wanting in Australia. Kangaroos were very important sources of food-supply to the natives, and are hunted by the colonists, both for sport and with a view to their destruction, on account of the damage they naturally do in consuming the grass, now required for feeding cattle and sheep. Notwithstanding this, they have in some districts increased in numbers, owing to the suppression of their former enemies, the aborigines and the Dingo or native dog. A few species are found in New Guinea and the adjacent islands, which belong, in the zoological sense, to the Australian region.

Before noticing the various generic types of the _Macropodidæ_, a few words are necessary in respect of the tooth-change, and we may here quote the observations of Mr. O. Thomas on this subject. “The full dentition of the members of this family consists, in the upper jaw, first of three incisors, then of a small canine (often, however, suppressed, as in Fig. 55), and then of six cheek-teeth, of which the second in the series is the only one which has a milk or deciduous predecessor, and is therefore the one to be regarded as the last premolar of the typical mammalian dentition. The special characteristics that render the development and succession of the teeth in the _Macropodidæ_, and especially in the genus _Macropus_, so puzzling to systematic zoologists, are: firstly, a general progression forwards in the jaw of the whole tooth-row, comparable to that found elsewhere only in the Elephants and some Sirenians; and, secondly, the fact that before the tooth-change the first tooth of the series (_p_ 3) and the single milk-tooth (_dm_ 4) placed next to it, both of which fall out at the change, are respectively so very similar in shape and size to the first and second teeth of the permanent series, viz. the permanent premolar (_p_ 4) and the first molar (_m_ 1), as to be most naturally mistaken for, or compared with, them in specific descriptions.... The necessary knowledge as to the stage of dentition in which any skull may be, can often be gained only by cutting open the bone either above and behind the first tooth of the series to see if the true permanent _p_ 4 be still buried there (in which case, of course, that first tooth is only _p_ 3), or behind the last visible molar to see if there be yet another tooth behind it, showing it to be _m_ 3 and not _m_ 4. The first plan is, as a rule, the better, since _p_ 4 is generally by far the most important tooth for diagnostic purposes, and its characters have, therefore, in any case to be taken into account.”

The _Macropodidæ_ are divided into three well-marked sections: (1) the true Kangaroos (_Macropodinæ_); (2) a group consisting of smaller animals, commonly called Rat Kangaroos, or (improperly) “Kangaroo Rats,” or sometimes Potoroos; and (3) the _Hypsiprymnodontinæ_, now represented only by a single species.

Subfamily =Hypsiprymnodontinæ=.—Size very small. Claws small, feeble, and subequal. Hind feet with an opposable hallux. Tail naked and scaly. The fourth premolar twisted obliquely outwards, as in _Phalanger_. Other teeth as in the _Potoroinæ_.

This subfamily is now represented only by the genus _Hypsiprymnodon_,[68] which is a form of great interest, as showing a structure of foot connecting that of the Kangaroos with that of the Phalangers. The single known species, _H. moschatus_, was described by Ramsay from specimens discovered in north-east Australia. It was described almost simultaneously by Owen under the name of _Pleopus nudicaudatus_. From the resemblance in the structure of the foot and the obliquity of the premolars to the Phalangers Mr. Thomas has some hesitation as to which family should receive this genus, but the macropine characters of the mandible preponderate in favour of the _Macropodidæ_.

_Triclis._[69]—A lower jaw of a much larger form from the Pleistocene deposits of Australia apparently indicates another member of this subfamily, having the outwardly directed and grooved premolar characteristic of _Hypsiprymnodon_. It differs, however, from that genus, and also from all other known _Macropodidæ_, in having a small tooth between the incisor and fourth premolar, which apparently represents a canine, or perhaps an anterior premolar. This form indicates, therefore, a closer connexion between the _Phalangeridæ_ and _Macropodidæ_ than any other.

Subfamily =Potoroinæ=.—The second section or subfamily, the _Potoroinæ_, have the first upper incisor narrow, curved, and much exceeding the others in length (Fig. 54). Upper canines always persistent, flattened, blunt, and slightly curved. Premolars of both jaws always having large, simple, compressed crowns, with a nearly straight or slightly concave free cutting edge, both outer and inner surfaces usually marked by a series of parallel, vertical grooves and ridges, these teeth being either set in the same line with the molars, or slightly bent outwards. Molars with quadrate crowns, having a blunt, conical cusp at each corner, the fourth notably smaller than the third, sometimes rudimentary, and appearing early. Fore feet narrow; three middle toes considerably exceeding the first and fifth in length; their claws long, compressed, and but slightly curved. Hind feet as in _Macropus_. Tail long and hairy, sometimes partially prehensile, being used for carrying bundles of grass with which these animals build their nests.

[Illustration: FIG. 54.—Skull and teeth of Rat Kangaroo (_Bettongia lesueuiri_). _c_, Upper canine. The other letters as in Fig. 51.]

The Potoroos or Rat Kangaroos are all small animals, none of them exceeding a common rabbit in size. They inhabit Australia and Tasmania, are nocturnal, and feed on the leaves of various kinds of grasses and other plants, as well as roots and bulbs, which they dig up with their fore paws. Nine species are known, presenting a considerable range of diversity in minor characters, and admitting of being grouped in four principal sections, which may be allowed the rank of genera. These are:

_Potorous._[70]—Head long and slender. Auditory bullæ somewhat inflated. Ridges on premolars few and perpendicular. Large palatine foramina. Tarsus short. Muffle naked. Three species, viz. _P. tridactylus_, _P. gilberti_, and _P. platyops_; the last two being confined to West Australia.

_Bettongia._[71]—Head comparatively short and broad. Ears short and rounded. Auditory bullæ generally much inflated. Large palatine foramina. Tarsus long. Ridges on premolars numerous and oblique. Tail more or less prehensile, thickly haired, and the hairs on the upper surface longer than those on the lower, and forming a crest. Muffle naked. Four species, viz. _B. penicillata_, _B. cuniculus_, _B. gaimardi_, _B. lesueuiri_.

_Caloprymnus._[72]—Muffle naked, as in _Bettongia_, but the edge of the hairy part less emarginate backwards in the middle line. Ears short, rounded, and hairy. Auditory bullæ much inflated, and of large size. Nasals larger and wider behind than in the other genera. Very long anterior palatine foramina. Limbs as in _Bettongia_. Tail thin, cylindrical, evenly coated with short hair, without trace of a crest. Skull broad and flat, with a remarkably short and conical muzzle. The sole representative of this genus is _C. campestris_ of South Australia, originally referred to _Bettongia_.

[Illustration: FIG. 55.—Skull and Teeth of the Red-necked Wallaby (_Macropus ruficollis_). _i¹_, _i²_, _i³_, First, second, and third upper incisors; _pm_, fourth or posterior premolar (the penultimate or third having been already shed); _m¹_, _m²_, _m³_, _m⁴_, the four true molars. The last, not fully developed, is nearly concealed by the ascending ramus of the jaw.]

_Æpyprymnus._[73]—Head short and broad. Auditory bullæ not inflated. No palatine foramina. Tarsus long. Muffle partially hairy. Tail evenly hairy, not crested above. Molars oblong, less distinctly quadritubercular, and not decreasing so much in size posteriorly as in the other genera. Represented only by _Æ. rufescens_.

Remains of _Æ. rufescens_ occur in the Pleistocene cave-deposits of New South Wales.

Subfamily =Macropodinæ=.—This subfamily includes the largest forms. The cutting edges of the upper incisors are nearly level, or the first pair but slightly longer than the others (Fig. 55). The canines are rudimentary and often wanting. The premolars are usually not longer (from before backwards) than the true molars and less compressed than in the last subfamily; they are placed in precisely the same line with the molars. The crowns of the molars always have two prominent transverse ridges; and these teeth increase in size from before backwards, the fourth molar appearing very late. The fore limbs are small, with subequal toes armed with strong, moderately long, curved claws. Hind limbs very long and strongly made. Head small, with more or less elongated muzzle. Ears generally rather long and ovate.

Upwards of forty-four existing species of this group have been described, and many attempts have been made to subdivide them into smaller groups or genera for the convenience of arrangement and description, but these have generally been based upon such trivial characters that it is preferable to speak of many of them as sections of the genus _Macropus_, reserving generic rank only to forms somewhat aberrant in structure. According to this arrangement the genera will be as follows:

_Lagostrophus._[74]—Represented only by the Banded Wallaby (_L. fasciatus_) of Western Australia, which presents the following distinctive features. Size small. Muffle naked. Hind feet covered with long bristly hairs, concealing the claws. Lower part of back marked by dark cross-bands. Skull with a narrow pointed muzzle and inflated auditory bullæ; symphysis of mandible firmly united. No canine. Upper incisive series meeting at a sharp angle, and diverging but slightly behind. First incisor smaller in section than either of the others and scarcely longer, bluntly pointed; second with a flattened oral surface; third smaller, similarly flattened, but with a groove on oral surface forming a notch at its postero-external angle. Fourth premolar short, with a distinct inner ledge. Molars as in _Macropus_.

_Dendrolagus._[75]—General proportions of limbs and body normal and unlike those of other members of the family. Muffle broad and only partly naked. Fur on nape, and sometimes on back, directed forwards. Fore limbs nearly as large as the hind; hind feet with the syndactylous second and third digits relatively large; claws of fourth and fifth hind digits curved like those of the manus. Tail very long, and thickly furred. Skull stout, with a short and wide muzzle; the posterior part of the palate fully ossified, and the auditory bullæ not inflated. A small canine. Fourth premolar large, but much shorter antero-posteriorly than in the next genus; molars as in the latter.

This genus includes four species of Tree-Kangaroos, three of which occur in New Guinea, while _D. lumholtzi_ is found in North Queensland. They differ greatly from all the other forms in being chiefly arboreal in their habits, climbing with facility among the branches of large trees, and feeding on the bark, leaves, and fruit. They are confined to the tropical forests of the regions mentioned; and it would appear that we must regard their resemblance in the proportions of the limbs and habits to the Phalangers as having been independently acquired.

_Dorcopsis._[76]—Hind limbs relatively less large than in _Macropus_. Muffle large, broad, and naked. Ears small. Fur on nape directed wholly or partially forwards. Hind claws not concealed by hair. Tail with a nearly naked tip. Skull long and narrow, with the auditory bullæ not inflated. A well-developed canine. First upper incisor somewhat short; second and third nearly equal, notched externally. Fourth premolar greatly elongated antero-posteriorly, its length generally exceeding the united lengths of the first and second molars; a distinct inner ledge, and vertical grooves on both sides. Molars low and rounded, with the median longitudinal bridge between the ridges almost or quite aborted, and the talon in front of the first transverse ridge very narrow, and not extending to the inner side. The two series of cheek-teeth parallel, or nearly so, instead of converging at the extremities.

Three species of this genus are known, all of which are from New Guinea; the type being _D. muelleri_. In the characters of the dentition, the forward inclination of the fur on the nape, and other points, this genus is allied to _Dendrolagus_; but _Dorcopsis macleayi_ connects the other species with _Macropus_.

_Lagorchestes._[77]—Muffle entirely or partially covered with hair. Fourth hind digit with a long claw, not concealed by hair. Tail rather short, evenly furred, without a spur. Skull with short muzzle and diastema, and inflated auditory bulla. Canine present, sometimes very small. Fourth premolar large, not constricted in the middle, with a continuous inner ledge.

This genus includes the Hare-Kangaroos, a group of small hare-like animals, great leapers and swift runners, which mostly affect the open grassy ridges, particularly those of a stony character, sleeping in forms or seats like the common hare. Their limbs are comparatively small, their claws sharp and slender, and their muffle is clothed with velvet-like hairs. Three species—_M. leporoides_, _M. hirsutus_, _M. conspicillatus_.

The range extends over the whole of Australia, but does not embrace Tasmania.

_Onychogale._[78]—Muffle hairy. Fourth hind claw long, narrow, compressed, and sharp. Tail long and tapering, covered with short hair, and furnished at the tip with a horny spur. Skull nearly as in _Macropus_, with the auditory bullæ more or less inflated. Canine small or wanting. Upper incisors small, decreasing in size from first to third. Fourth premolar small, hour-glass shaped, and without inner ledge. Molars as in _Macropus_.

This genus contains three species, having the same distribution as _Lagorchestes_. Mr. O. Thomas observes: “The spur-tailed Wallabies form a natural little group, distinguished both by the shape of the incisors and the peculiar horny excrescence at the tip of the tail. The latter character is altogether unique among Marsupials, and is only found among other mammals in the Lion, which occasionally has a somewhat similar horny spur at the end of its tail. In the case of the Wallabies it is difficult to conceive what can be the use of this spur; and observations on the living animal are much needed with regard to this interesting point.”

_Petrogale._[79]—Muffle naked. Fur of nape directed backwards. Claw of fourth hind digit very short. Tail long, cylindrical, thinner than in _Macropus_, and thickly haired and pencilled at the extremity. Skull as in the smaller species of _Macropus_, with large posterior palatal vacuities, and the bullæ sometimes inflated. No canine. Upper incisors small, the third resembling that of _Macropus_. Fourth premolar large and stout, as in some of the Wallabies, with a continuous inner ledge, and two or three indistinct vertical ridges externally. Molars as in the Wallabies.

This genus is represented by six species, of which _P. penicillata_ is a well-known example, ranging over the whole of the mainland of Australia. The Rock-Wallabies, as its members may be called, are very closely allied to some of the true Wallabies; and some hesitation may be expressed as to the advisability of accepting their generic separation from _Macropus_. They inhabit rocky regions, making their retreats in caverns and crevices, leaping with surprising agility from one narrow ledge to another, and browsing upon the scanty herbage that the neighbourhood of such situations affords. The species are _P. xanthopus_, _P. penicillata_, _P. lateralis_, _P. concinna_, _P. brachyotis_, _P. inornata_.

Remains of _P. penicillata_ are found in a fossil state in the Pleistocene cave-deposits of New South Wales.

_Macropus._[80]—Muffle generally completely naked. Ears large. Fur on nape (with an occasional exception in two species) directed backwards. Claw of fourth hind digit very long. Tail thick, tapering, and evenly furred. Four mammæ. Skull (Fig. 55) long, smooth, and rounded; the nasals expanded behind; generally large palatal vacuities; and the auditory bullæ not inflated. Canine minute, and shed at an early period. Incisor series forming an open curve; the first the tallest, and the third nearly always the longest antero-posteriorly, and generally with an infolding of enamel near its postero-external angle. Fourth upper premolar with a secant edge, and an inner basal ledge or tubercle; corresponding lower tooth secant; both maybe longer or shorter than first molar. Molars (except very occasionally) with a distinct longitudinal bridge connecting transverse ridges. Lower incisors long and scalpriform, with inner secant edges opposable, owing to the loose articulation of the mandibular symphysis.

This genus includes the true Kangaroos and Wallabies, the size of the individual existing species varying from that of a Rabbit to that of a Man. There are no less than twenty-three existing species, which may be divided into three groups, as well as many extinct ones. The genus is found in Australia and New Guinea, as well as in the eastern half of the Austro-Malayan transitional region.

The first group, or true Kangaroos, comprises the largest existing forms, which are generally of a uniform and sombre colour.

The skull is of a large and massive type, with the palate more or less well ossified posteriorly, while the molars frequently have a median longitudinal bridge connecting the first transverse ridge with the anterior talon, and no antero-external bridge between the same ridge and talon. The history of the discovery of the typical representative of this group, as being of considerable interest, may be given at some length. When Captain Cook, during his first memorable voyage of discovery, was detained for the purpose of refitting his ship at Endeavour river on the north-east coast of Australia, a strange-looking animal, entirely unknown to them, was frequently seen by the ship’s company; and it is recorded in the annals of the voyage that, on the 14th of July 1770, “Mr. Gore, who went out this day with his gun, had the good fortune to kill one of the animals which had been so much the subject of our speculation, ... and which is called by the natives kanguroo,” a name which, though it does not appear to be now known to any of the aboriginal tribes of the country, has been adopted for this animal in all European languages, with only slight modifications of spelling. With the exception of a passing glimpse in the beginning of the same century by the Dutch traveller Bruyn of some living examples of an allied species, this was the first introduction to the civilised world of any member of a group of animals now so familiar. The affinities of the species, skins of which were brought home by Captain Cook and subsequent voyagers, were recognised by Schreber as nearer to the American opossums (then the only known Marsupials) than to any other mammals with which zoologists were acquainted, and consequently it was placed by him, in his great work on the Mammalia, then in the course of publication, in the genus _Didelphys_, with _gigantea_ for a specific designation,—the latter having been bestowed upon it by Zimmermann under the impression that it was a huge species of jerboa. Soon afterwards (1791) Dr. Shaw very properly formed a new genus for its reception, which he named _Macropus_, in allusion to the peculiar length of its hind foot. By the name thus formed, _Macropus giganteus_, this kind of Kangaroo has ever since been known in zoological literature. It is the common Gray Kangaroo, called “boomer,” “forrester,” or “old man” by the colonists, and frequents the open grassy plains of the greater part of eastern Australia and Tasmania; a figure being given in the woodcut on p. 160. The muffle is partly covered with hair, and the fourth premolar very short. Several varieties are known.

A sub-group, distinguished from the above by the naked muffle, includes some very large and handsome species, which principally dwell in rocky mountain ranges, as _M. rufus_, the great Red Kangaroo, _M. antilopinus_, and _M. robustus_. The fourth premolar is of large or medium size in these forms. Remains of _M. giganteus_ occur fossil in the Pleistocene of Australia, where we also find the allied extinct _M. titan_, which attains somewhat larger dimensions. _M. robustus_ also dates from the same geological epoch, where it was accompanied by two allied types known as _M. altus_ and _M. cooperi_.

The second group includes the larger Wallabies, which are smaller than the true Kangaroos, with a brighter and more variegated coloration. The palate is generally more incomplete than in the typical group; and in the molars the anterior talon is connected with the first transverse ridge by an external instead of a median longitudinal bridge. The members of this group are frequenters of forests and dense impenetrable brushes and scrubs, and hence are often called Brush Kangaroos, though a native name, “Wallaby,” is now generally applied to them. There are several species, of which _M. ruficollis_, _M. ualabatus_, _M. parryi_, and _M. agilis_ are the best known.

_M. ualabatus_ and _M. parryi_ are found fossil in the Pleistocene deposits of Australia. In those beds we also meet with remains of several very large extinct species, which appear to be allied to those Wallabies in which the fourth premolar is large and elongated, all of them agreeing with the Wallabies in the absence of the median bridge between the first ridge and talon of the molars. These fossil forms comprise _M. brehus_, in which the skull was probably about one foot in length, and _M. rœchus_, and _M. anak_, which were of somewhat inferior dimensions. In the last-named species the length of the fourth upper premolar is equal to that of the first and half of the second molar.[81]

The third and last group of the genus includes the small Wallabies, which are small and lightly-built animals, in some instances not larger than a Rabbit. Their muffles are always naked, and in the skull the anterior palatine foramina are small and the posterior vacuities very large, while the posterior expansion of the nasals is very marked. The third upper incisor is smaller than in the last group. This group extends farther into the tropics than either of the others, being found in the New Britain and Aru islands, as well as in New Guinea. _M. brachyurus_ is remarkable for its comparatively short and slender tail and small ears. The earliest known species of Kangaroo, referred to before, _M. bruni_, belongs to this section. Several examples were seen by Bruyn in 1711 living in captivity in the garden of the Dutch governor of Batavia, and described and figured in the account of his travels (_Reizen over Moskovie_, etc.) under the name of “Filander.” It was quite lost sight of, and its name even transferred by S. Müller to another species (_Dorcopsis muelleri_), until rediscovered in 1865 by Rosenberg, who sent a series of specimens to the Leyden Museum from the islands of Aru and Great Key, thus determining its true habitat. _M. thetidis_ is a well-known Australian representative of this group.

_Extinct genera._—In addition to the fossil forms already mentioned which can be referred to existing genera, there are others from the Australian Pleistocene indicating extinct generic types of _Macropodidæ_, to which brief reference may now be made. The first of these is _Sthenurus_,[82] represented by a single large species (_S. atlas_), and characterised by the presence of a complete inner lobe to the fourth upper premolar, and of an outer one in the opposing lower tooth, so that these teeth present a flat and oval grinding surface when worn. The median longitudinal bridge connecting the transverse ridges of the molars is very imperfect; and in the upper molars there is no bridge between the first ridge and talon. In _Procoptodon_[83] the premolars resemble those of _Sthenurus_, but the molars are elongated, and usually have their enamel thrown into numerous vertical foldings. The most distinctive feature is, however, the complete ankylosis of the mandibular symphysis; the mandibular rami being deep, and the diastema in the dental series short. The lower incisors are nearly cylindrical, and the palate has large vacuities. Three species are known. The largest representation of the whole family is the type of the genus _Palorchestes_[84] (_P. azael_), in which the length of the skull is estimated at sixteen inches. It is distinguished from _Procoptodon_ by the longer mandibular symphysis and diastema, and the spatulate lower incisors. The true molars have no distinct anterior talon, and are not grooved, while the palate was fully ossified.

EXTINCT FAMILIES.

Here may be noticed two genera of extinct Marsupials, the remains of which have been found in the Pleistocene deposits of Australia, which agree with the _Macropodidæ_ and the _Phalangeridæ_ in having ³⁄₁ incisors, those of the lower jaw being very large and proclivous. As the whole of their structure, especially that of the hind feet, is not yet known, their precise affinities cannot be determined.

_Diprotodon._[85]—Dentition: _i_ ³⁄₁, _c_ ⁰⁄₀, _p_ ¹⁄₁, _m_ ⁴⁄₄; total 28. The first upper incisor very large and scalpriform (Fig. 56). True molars with prominent transverse ridges, as in _Macropus_, but wanting the longitudinal connecting bridge. Anterior and posterior limbs less disproportionate than in the Kangaroos. Humerus elongated, and differing from that of nearly all Marsupials in the absence of an entepicondylar foramen. The palate is fully ossified, and there is no pit or perforation in the masseteric fossa of the mandible. _D. australis_ is the largest known Marsupial, being fully equal in bulk to a Rhinoceros. It may be regarded as the type of a family—_Diprotodontidæ_—having affinity on the one hand with the Phalangers and on the other with the Kangaroos.

[Illustration: FIG. 56.—Left lateral aspect of the skull of _Diprotodon australis_; from the Pleistocene of Australia. ⅒ natural size. _i_, Incisors; _p_, premolar; _m_, molars. (After Owen.)]

_Nototherium._[86]—Represented by a species of somewhat smaller size than the type of _Diprotodon_, with a shorter skull, in which the zygomatic arches are very wide and the nasals curiously expanded at their extremities. The mandibular symphysis is ankylosed; and, as in _Diprotodon_, there appears to have been no tooth-change. The humerus probably referable to _Nototherium_ is of a short and widely expanded type, with a large entepicondylar foramen, and coming nearer to that of the Wombat than to that of any other existing form. The _Nototheriidæ_ may apparently be regarded as a distinct family connecting the _Diprotodontidæ_ with the _Phascolomyidæ_ and _Phalangeridæ_.

_Bibliography of Marsupialia._—G. R. Waterhouse, _Nat. Hist. of the Mammalia_, vol. i. “Marsupiata,” 1846; J. Gould, _Mammals of Australia_, 1863; R. Owen, article “Marsupialia,” in _Cyclop. of Anatomy and Physiology_, and various memoirs “On Extinct Mammals of Australia” in _Philosophical Transactions_; W. H. Flower, “On the Development and Succession of the Teeth in the Marsupialia,” _Phil. Trans._ 1867; O. Thomas, “On the Homologies and Succession of the Teeth in the Dasyuridæ,” _Phil. Trans._ 1887; and “Catalogue of Marsupialia and Monotremata in the British Museum,” 1888.