_Myrmecobius_ is so different from the last-described genera (DASYURINAE) that it is usually separated from them as a sub-family MYRMECOBIINAE. The animal is of a bright rufous colour, banded posteriorly with white. There is no hallux, though the metatarsal belonging to that digit is present. There are four mammae.[94] On the chest is a naked patch of some extent, upon which open the ducts of a complex gland, which has been described and figured by myself.[95] There is no pouch, but a tract of skin shows indications of a pouch-like structure. The teeth are extraordinarily numerous, fifty to fifty-four; the formula being I 4/3(4) C 1/1 Pm 3/3 M 5/6. Their resemblance to those of certain Jurassic Marsupials is dealt with on p. 100.[96] In this matter lies of {155} course the chief interest of the genus, which may be "an unmodified survivor from Mesozoic times, and therefore from a time long before the Didelphyidae, Peramelidae, and Dasyuridae were differentiated one from the other." Another ancient feature (found in Jurassic mammals) is a mylo-hyoid groove upon the lower jaw, which, however, is not always present, and its existence has therefore been denied. The single species, _M. fasciatus_, is partly arboreal and partly terrestrial in habit, and feeds upon ants. It is a Western and Southern Australian form. [Illustration] FIG. 82.--Banded Australian Anteater. _Myrmecobius fasciatus._ x 1/5. FAM. 2. DIDELPHYIDAE.--All the members of this family are pentadactylous. The teeth are fifty in number, arranged thus: I 5/4 C 1/1 Pm 3/3 M 4/4. The caecum is small; the pouch is generally absent; the tail generally long and prehensile. [Illustration] FIG. 83.--Virginian Opossum. _Didelphys virginiana._ x 1/5. (After Vogt and Specht.) The genus _Didelphys_ contains most of the forms belonging to this family, including as it does some twenty-three species. The Opossums are mainly arboreal animals, insectivorous in their food; but the larger species eat reptiles, birds, and their eggs. Several of the small species carry their young, when able to leave the teats, on {156} their back, the tails of the young being wrapped round that of the mother. It is not only the pouched species which carry their young in something of this fashion. Azara's Opossum, an animal as big as a cat, is said to carry its eleven young ones (themselves as large as rats) on the back, though their foothold does not appear to be strengthened by intertwining the tails. Even with this huge family on her back, the mother can climb trees with considerable alacrity. The mammae are seven to twenty-five in number. The genus has been lately split up into a number of genera, _Marmosa_, _Dromiciops_, _Peramys_, etc. [Illustration] FIG. 84.--Thick tailed Opossum. _Didelphys crassicaudata._ x 1/5.