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.