1 62 MARSUPIALIA 



molar (m 1), as to be most naturally mistaken for, or compared with, 

 them in specific descriptions. . . . The necessary knowledge as to 

 the stage of dentition in which any skull may be, can often be 

 gained only by cutting open the bone either above and behind the 

 first tooth of the series to see if the true 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 Macropodidce are divided into three well-marked sections : 

 (1) the true Kangaroos (Macropodince) ; (2) a group consisting of 

 smaller animals, commonly called Rat Kangaroos, or (improperly) 

 " Kangaroo Rats," or sometimes Potoroos ; and (3) the Hypsipryrrir 

 nodontince, now represented only by a single species. 



Subfamily Hypsiprymnodontinse. — Size very small. Claws 

 small, feeble, and subequal. Hind feet with an opposable hallux. 

 Tail naked and scaly. The fourth premolar twisted obliquely out- 

 wards, as in Phalanger. Other teeth as in the Potoroince. 



This subfamily is now represented only by the genus Hypsi- 

 prymnodon, 1 which is a form of great interest, as showing a structure 

 of foot connecting that of the Kangaroos Avith that of the Phalan- 

 gers. 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 Maoropodiace. 



Triclis.' 2 — A lower jaw of a much larger form from the Pleisto- 

 cene deposits of Australia apparently indicates another member of 

 this subfamily, having the outwardly directed and grooved pre- 

 molar characteristic of Hypsiprymnodon. It differs, however, from 

 that genus, and also from all other known Macropodidce, 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 

 Phalangeridce and Macropodidce than any other. 



Subfamily Potopoinse. — The second section or subfamily, the 

 Potoroinm, have the first upper incisor narrow, curved, and much 

 exceeding the others in length (Fig. 54). Upper canines always 

 persistent, flattened, blunt, and slightly curved. Premolars of both 



1 Ramsay, Proc. Linn. Soc. K. S. Wales, vol. i. p. 33 (1876). 

 2 De Vis, Proc. Roy. Soc. Queensland, ser. 2, vol. iii. p. 8 (1888). 



