OF TJIE AUSTEALIAN MAESUPIALIA. 135 



canines, and a varying number of undifferentiated cheek-teeth, all of whicli are vestigial *. 

 The upper incisors are usually two in number, judging from four specimens in the 

 collection, and are always extremely minute and styliform. Apart from their minute 

 size, the upper canines bear a certain resemblance to those of Dromicla in being only 

 slightly curved and rounded at the tips. The median lower incisors are almost straight 

 and extremely slender, but are otherwise of the usual diprotodont type. The cheek- 

 teeth (PI. 6. fig. 24), like the upper incisors, are minute and cither simply styliform or 

 slightly curved. Their number apjicars to be usually three, and their homologies are 

 indeterminable. 



The exact dental relations of Tarsipes with the remaining Phalangeridse are doubtful, 

 and its mode of origia can only be conjectured from the association of its reduced 

 dentition with its mellivorous habit. It is extremely probable that the omnivorous 

 evolution of the Phalangeridte began with diminutive animals which, like Acrobaten, 

 Disioechui-us, and Bromicia, were able to live among the smaller branches of trees, and 

 to supplement their insectivorous fare with blossoms and honey. Certain of these must 

 have continued the omnivorous evolution in a normal way, giving rise to the Phalau- 

 gerinoe and Phascolarctinai, while others resorted largely to a mellivorous habit, giving 

 rise to Tarsipes-\. The reduction of the dentition is due to the same cause as in 

 ant-eating forms, the food requiring no mastication, and its collection being perfectly 

 provided for by the prehensile development of the tongue. 



Phascolarctin^. * 



The three genera forming the present division are of general interest as presenting a 

 fresh instance of the remarkable parallelisms between marsupial and placental types. 

 In the MacropodidoB, and in their prototypes the Phalangerinoe, wc have two groups, 

 roughly distinguishal)le by the hypsilophodont and brachybunodont moditications of thi^ 

 molars. In respect to these modifications the two groups parallel the perissodactyl 

 Ungulata, especially the tapiroid representatives of the latter, and the Condylarthra. 

 The PhascolarctiucB now present selenodont modifications similar to those of the 

 artiodactyl Ungulata, especially the more primitive forms which retain the brachyodont 

 condition. 



In the case of the Marsupials the evolution of the selenodont section is of very 

 limited extent, the reason being that, unlike the case of the bunodont PhalangerintP, 

 none of the members of the original arboreal stock have given rise to terrestrial 

 successors. The evolution of the bunodont section would be scarcely less limited were it 

 not for the existence of the terrestrial Macropodidte, Phascolomyidtv, and Diprotodontidas. 



With regard to their special relationships, the dental characters indicate that the 

 genus Pseudochirm represents the ancestral type from which the remaining genera 

 Fetau7'oides and Phascolurctus have been derived. Like Phalanger, Pseudochiriis is 



* C/. Waterhouse (1846). 



t The interesting observation of Uould (1863) with reference to the fly-catchiDg propensities of a captive Tai-sipex 

 may he noted in this connection. 



