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.