LIFE HABITS AND DENTITION 83 



merely vestigial. All other intermediate lower teeth in ad- 

 vance of the last premolar are eliminated. The npper molars 

 show protocone, paracone, metacone and hypocone and from 

 the first and last mentioned cnsps which are connected by a 

 low ridge there rnn ledges round the anterior and posterior mar- 

 gins of the tooth as in Petanrus but more strongly marked. All 

 trace of styles has vanished. The hypocone is not developed on 

 the last molar. Transverse ridges are well marked between 

 protocone and paracone and between hypocone and metacone. 

 Of the mandibular molars the first still shows some sectorial 

 traits because of the relative prominence of the protoconid and 

 the vestigial character of the metaconid. In the others the loss 

 of the paraconid is obvious, although a remnant of the proto- 

 conid-paraconid ledge remains to form a triturating surface 

 upon which the hypocone of the upper tooth next in. front may 

 play. The heel exhibits two well-marked cusps, the entoconid 

 and the hypoconid, the latter of which is connected with the 

 protoconid by a slight ridge. From the hypoconid a small 

 ledge runs round the posterior border of the crown. 



Before passing on to the lophodont Kangaroos we must note a 

 type of purely herbivorous dentition with crescent cusped molars 

 presented in the so-called crescent-toothed Phalangers. Of 

 these the most advanced species is Phascolarctos cinereus, the 

 Koala or Native Bear (Fig. 24). This heavily built animal of 

 the size and somewhat of the appearance of a poodle dog is 

 never seen in captivity outside Australia because of the im- 

 possibility of obtaining the proper food. The animal lives 

 largely upon leaves of the blue gum tree though it also de- 

 scends to the ground at night to dig for roots. Its diet is thus 

 purely herbivorous. The tooth formula is: 



I T , C^,P T ,M--. total 30. 

 I U 1 4 



The dentition is at once distinguished from that of the Pha- 

 langer by the absence of the rudimentary lower second incisors, 

 the elimination of more antemolar teeth, the retention of styles 



