belonging to the Order Rodentia. 131 
Muridæ ; on the hind feet there are three toes on the same line and of the 
same length, and at a considerable distance behind these, a well-developed 
interrial toe, furnished with a distinct claw, and apparently a smaller or rudi- 
mentary one, without a claw, on the outer side of the tarsus. Of this latter, 
however, I am by no means certain, for it is difficult to distinguish, in a 
Sketch, like that from which the principal part of this description has 
been taken, the difference between a rudimentary toe of this nature, and 
the small fleshy pads usually found on the soles of such animals. If it 
exist at all, however, the external toe in question must be a mere tubercle ; 
but for my own part, though I have here thought proper to describe the 
appearance exactly as I have observed it in the sketch, I should rather be 
inclined to doubt its existence, because rudimentary toes of that description, 
where they do exist, are generally found on the inner side of the foot, and I 
do not remember having ever met with a single example of such a clawless 
tubercle on the outer surface. In either case the character of the toes will 
readily distinguish the Dipus Mitchellii from the rest of its congeners; there 
is no known Jerboa which has a clawless or tuberculous toe on the hind feet ; 
and the only other species with which it could possibly be confounded, the 
Dipus tetradactylus of Lichtenstein, has the additional toe on the external 
instead of the internal surface of the tarsus. That species is indicated as an 
inhabitant of the Libyan desert, where it was found by Drs. Hemprich and 
Ehrenberg; the five-toed species are all natives of the plains of Central Asia 
and Southern Siberia, and it is not a little singular that we should find the 
same type reproduced in the interior of Australia. The Dipus Mitchellii was 
found at Reedy Plains, near the junction of the Murray and the Murrum- 
bidgee, on the northern boundaries of Australia Felix. 
But I may be asked for a further justification of the opinion here announced, 
as to the existence of a true Dipus in Australia, founded as this opinion is 
upon the authority of a mere drawing ; and I confess that the question is both 
just and pertinent. It might, indeed, be suspected, with some show of pro- 
bability, that since the country is already known to abound in Saltigrade 
Marsupials, the animal in question may really belong to that form, and be 
more nearly allied to the Kangaroo rats than to the Rodentia. That the 
animal may eventually turn out to be Marsupial is not impossible ; but, inde- 
