AUSTRALIAN NATURAL HISTORY. 139 



Below, tlie Thylacoleo has generally two or three small teeth, 

 sometimes on the inner side of the great premolar, which rejDre- 

 sents the diminutive canine and premolars No. 1 and No. 2. The 

 shape of these small and functionless teeth is not known, as all 

 the specimens of mandibles in collections show only empty 

 sockets. 



Eam. Phalangistid^. 



The phalangers proper, whereof the Thylacoleo is an aberrant 

 form, comprise animals the molar dentition of which is very 

 different in the seA^eral genera composing the family. They all 

 possess, however, the six incisors above and two iDelow ; their 

 canines are always well developed in the upper jaw, and the 

 molars have tapering fangs or roots. The living genera and 

 species are represented by the genus Cuscus, a northern form, in 

 many respects resembling the extinct Thylacoleo ; the genus 

 Dactylopsila, with greatly developed front cutting teeth and 

 small grinders ; the common ilying phalangers, or sugar squirrels, 

 of the genus Belideus, with small and slightly tuberculated 

 molars ; the feather-tailed genus, Acrolata, with much developed 

 canines, and with grinders reduced to three above and below in 

 each ramus ; the phalangers known as " opossums," of the genus 

 Phalangista, with a powerful third premolar turned more or less 

 outwards, to which (and not to the kangaroo rat premolar) the 

 great tooth of Thylacoleo bears a close resemblance, and the 

 ring-tailed phalangers of the genus Pseudoclieirus which close 

 the phalanger series proper. These animals, generally called 

 ring-tailed 'possums, resemble in their dentition the aberrant 

 Phascolarctos, or native bear ; and in the loosely anchylosed and 

 movable mandibles and the scooped out lower incisors, they 

 approach the kangaroos. 



The relationship between the two animals, the great ring-tail 

 flying squirrel and Cook's ring-tail phalanger or opossum, is so close 

 that I am often obliged to look and compare skulls of both, where 

 in other cases it is easy enough to feel without looking to which 

 genus a skull or jaw belongs. 



The Thylacoleo alone combines in its dentition, and in the form 

 of the mandibles, characteristics which are found scattered about 

 among the whole Phalanger and Bettong tribe. 



Sub-.Pamily Phascolarctodidcs. 



The presence of a second species of the genus Phascolarctos, 

 lately described by me in the Zoological Society's proceedings, 

 makes it necessary to establish a sub-family for their reception. 

 The dentition of this group is a very peculiar one, being chiefly 

 distinguished by the total absence of canine teeth below, and by 



