THE TRUE KANGAROOS AND WALLABIES 



1421 



small rounded ears, and long furry tails, of which the extremities are partially pre- 

 hensile in some of the species. Externally, the rat kangaroos cannot well be distin- 

 guished in general appearance from some of the smaller short-eared representatives 

 of the preceding group; and it is accordingly of prime importance that the foregoing 

 distinctive characteristics should be thoroughly understood. The group comprises 

 nine species, which are confined to Australia and Tasmania, and are divided into 

 four genera. 



The common rat kangaroo (Potorous tridactylus] , that figures in 

 the illustration on this page, may be taken as our representative 

 of the first of the four genera. The distinctive characteristics of the 

 genus being the long and slender form of the head, the few (three or four) perpen- 

 dicular ridges on the permanent premolar tooth in both jaws, the shortness of the 

 foot, the naked muzzle, and the rather large ears. In the skull the auditory bulla 



Common Rat 

 Kangaroo 



COMMON RAT KANGAROO. 



(One-sixth natural size. ) 



is somewhat swollen, and the unossified spaces in the palate are large. The figured 

 species, which is the largest of its genus, is confined to Eastern Australia and Tas- 

 mania, and is variable both in size and color; the length is, however, frequently 

 about fifteen inches, exclusive of the tail. It is specially characterized by the great 

 elongation of the muzzle; the general color of the coarse, long, and straight hair 

 being dark grizzled grayish brown, with a more or less marked tinge of rufous. 

 The West- Australian P. gilberti is a smaller allied form; while P. platyops, from the 

 same side of the continent, is still smaller, and has a broader and shorter muzzle. 



The brush-tailed rat kangaroo (Bettongia penicillata} , represented in 

 Brush-Tailed , -. . , 



Rat K - figure on p. 1422, appears to be the commonest and most widely 



spread of the group, and is one of four species having the following 

 characteristics in common. The head is comparatively short and wide, 

 with very small and rounded ears, and a naked muzzle; the foot is elongated; and 

 the permanent premolar tooth (figure on p. 1408) is characterized by its numerous 



garoo 



