The upper molar crowns, like those of the Cape golden mole, consist of very narrow V's, probably derived by ,degeneration from a more normal, less compressed type ; in the lower molars the talonids or hinder spurs are lost. A pouch is present and opens backward. A comparative study of the skeleton has shown that the marsupial mole resembles the Cape golden moles, which are true placental mammals, only in its "habitus," while its "heritage" is unmistakably that of other marsupials.
The hind feet are remarkably like those of kangaroos and have what was originally the fourth toe much elongated ; the first toe, if present, is small ; all the remaining toes have large pointed claws for scratching and digging. The hind foot also resembles those of kangaroos and other herbivorous marsupials in the fact that the toes corresponding to the second and third of the normal mammalian foot are very slender, much smaller than the fourth toe, and so closely appressed to each other that they appear to be united at their bases. Each, however, is a complete digit with its own claw and separate muscles. These two digits serve as a comb by which the animal removes from its fur biting lice or other unwelcome objects. This peculiar syndactylous specialization of the hind feet is found also throughout the series of diprotodont or herbivorous marsupials of Australia but not in any of the poly protodont families (American opossums, Australian dasyuroids, etc.).
The bandicoots have front teeth of the carnivorous-insectivor ous or polyprotodont type, essentially like those of the American opossums and the dasyuroids, while their molar teeth, although peculiar, show traces of derivation from some form in which the accessory cusps on the outer sides of the molar were strongly developed. The bandicoots, while chiefly insectivorous, frequently have the molar teeth much ground down by wear, which may indicate that their food gets mixed with a certain amount of grit. Apparently in adaptation to this condition, the molar teeth tend to acquire high crowns, like those of many rodents. Bandi coots are pugnacious little animals which leap up in the air and strike each other with their long-clawed hind-feet. In the forms with very long hind-feet this extraordinary leaping ability is probably useful not only in escaping enemies but in capturing in sects. All the species are now rapidly becoming rare. The family (Peramelidae) ranges from New Guinea and adjacent islands on the north to Tasmania on the south.
large number of species of highly diversified size and form, from the tiny dormouse phalanger to the almost elephantine extinct Diprotodon, and from the most agile pygmy "flying-squirrel" to the powerful and clumsy wombat.
The cuscus (Trichosurus vulpecula) of the islands northwest of Australia is often erroneously called an opossum. This mistake arises from the facts that both animals are pouched mammals, both live in trees, both have pointed muzzles and strongly grasp ing hands and feet and prehensile tails. But in many other im portant characters the American opossum and the Australian "opossum" differ widely. The former belongs to the polyprotodont division, having the incisors and canines disposed as in other car nivorous mammals, the latter have diprotodont front teeth, adapted for cutting vegetable fibre, and crested molar teeth adapted for grinding. Very striking is the contrast in the dental formulae of the two animals : The polyprotodont American opossums have no trace of the syndactylous specialization of the hind feet which, as described above, is so characteristic of the Australian "opossum" and there are many striking differences in the skulls and other parts of the anatomy. The Australian phalangers as a group live in close ecologic relations with the eucalyptus trees that dominate the landscape in all but the dryest regions of the interior. Many eat eucalyptus leaves and the "native bear" (Phascolarctos) normally lives on nothing else. To overcome the aromatic essence of these leaves and extract nutriment from this highly indigestible ma terial the phalangers have a long intestine and a greatly enlarged caecum. In locomotor habits the phalangers range from the sloth like native bear, which clings tenaciously to the branches with its large hands and feet, to the highly active flying phalangers, including several quite different genera, which have a skimming membrane on the sides of the body and between the limbs. In one division of the family, including Pseudochirus and Phasco larctos, the upper molar teeth each bear two sharp V's or cres cents. In another subfamily, which includes the Australian "opos sum" (Trichosurus), the two V's of the upper molars are modified into cross-crests. The last lower premolar of the typical phalangers has a compressed cutting crown, with more or fewer vertical grooves and ridges. In the phalangers, however, these cutting pre molars are not as elongate as they are in the smaller kangaroos. These cutting premolars, both in the upper and lower jaws, became greatly enlarged in the extinct "marsupial lion" (Thylacoleo), in which the molars were reduced and the front teeth became en larged and piercing. Sir Richard Owen was of the opinion that Thylacoleo was a fierce carnivorous creature but others have demurred from this opinion on various grounds and think the animal sheared some unknown kind of fruit. In widest contrast to the shearing-toothed Thylacoleo is the tiny long-snouted pha langer (Tarsipes) of West Australia, which is said to live on the honey and insects found in long-tubed flowers, into which it sticks its long muzzle and extensile tongue.