MARSUPIALS. 387 



sively increasing in length as they are placed forward. An inter- 

 space occurs between these and the canine, which is long, slender, 

 sharp-pointed, and recurved. The first incisor is longer than the 

 two behind, but is much shorter than the canine. In the lower 

 jaw the true molars are preceded by two functional false ones, 

 similar in size and shape to the three above the anterior false 

 molar, and the canine are represented by minute rudimental simple 

 teeth ; the single incisor is long and procumbent as in the other 

 Petaurists. 



With these differences of dentition approaching more or less 

 to one or other of the modifications of the dentition in the group 

 of Phalangers, the Petaurists may nevertheless be readily discrimi- 

 nated from those Phalangers which they most resemble ; for example, 

 the Petaurus Taguanoides may be distinguished from the Phalangista 

 Cookii by the greater relative length in the latter of the nasal and 

 maxillary portion of the skull ; while in most of the other species of 

 Petaurus, the facial part of the skull is relatively shorter than in the 

 Pet. Taguanoides. 



Genus Phascolarctus. — The absence of anomalous or functionless 

 premolars and of inferior canines appears to be constant in the only 

 known species of this genus. The dental formula (PI. 100, fig. 6.) in 

 three examples of the Koala f Phase, fuscus, Desm.) is 



Incisors — ; canines — : premolars — ; molars — : -= 30. 



1—1 ' 0—0 ' ^ 1— 1 ' 4—4 



The true molars are larger in proportion than in the Pha- 

 langers : each is beset with four three-sided pyramids, the cusps of 

 which wear down in age, the outer series in the upper teeth 

 being the first to give way ; those of the lower jaw are nar- 

 rower than those of the upper. The spurious molars are com- 

 pressed and terminate in a cutting edge ; in those of the upper jaw 

 there is a small parallel ridge along the inner side of the base. 

 The canines slightly exceed in size the posterior incisors ; they 

 terminate in an oblique cutting edge rather than a point ; their 

 fang is closed at the extremity ; they are situated as in the Pha- 

 langers close to the intermaxillary suture. The lateral incisors of 



c c 2 



