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. CHAPTER VII THE SUBCLASS EUTHERIA AND THE ORDER EDENTATA