250 POUCHED MAMMALS. 
tive of the first of the four genera. The distinctive characters of the genus being 
the long and slender form of the head, the few (three or four) perpendicular 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 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 Tasmania, 
and is variable both in size and colour; the length is, however, frequently about 
15 inches, exclusive of the tail. It is specially characterised by the great elonga- 
tion of the muzzle; the general colour of the coarse, long, and straight hair being 
dark grizzled greyish brown, with a more or less marked tinge of rufous. The 


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COMMON RAT-KANGAROO (4 nat. size). 
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. 
Brush-tailed The brush-tailed rat-kangaroo (Bettongia penicillata), repre- 
Rat-Kangaroo. sented in the figure on p. 251, 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. 237) is characterised by its numerous 
(fourteen or fifteen) and slightly oblique ridges. The tail is thickly furred, with 
the hairs longer on the upper than on the lower surface, and somewhat prehensile. 
In the skull the auditory bulla is generally much swollen; and the unossified 
spaces in the palate are large. The figured species is a somewhat smaller animal 
than the common rat-kangaroo; and is characterised by the great development of 
the tuft of hair on the upper surface of the end of the tail, of which the under 
surface is brown. It inhabits nearly all Australia, but is replaced in Tasmania by 
the much larger jerboa-kangaroo (B. cuniculus), in which the tail-tuft is scarcely 
developed. Lesueur’s rat-kangaroo (B. leswewr?), of which the skull is figured on 
p. 239, is a South and West Australian species distinguished from the one here 
figured by the small size of the tail-tuft, which is almost always white at the tip. 
