helnns'infr to the Order Rodentia. 131 



Miiridce ; 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 

 internal 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, tlic 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 tlie 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 Dipiis Mitcheliii from the rest of its congeners ; there 

 is no known Jerboa which has a clawless or tuberculous toe on the hind feet ; 

 and the oidy other species with which it could possibly be confounded, the 

 D'lpus 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 D'lpus MitehelUi was 

 found at Reedy Plains, near the junction of the Murray and the Murrum- 

 bidgee, on the northern boundaries of Australia Felix. 



13ut I may be asked foi- 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 impossihle : but, inde- 



