132 Mr. OaiLBY on certain Australian Quadrupeds, Sc. 
pendently of the express declaration of its discoverer, that it had no pouch, 
though he had. no recollection of the characters of the teeth, I beg leave, in 
the meantime, to offer the following reasons in support of my belief that it is 
a true Jerboa. In the first place, the form of the head, the swollen muzzle, 
covered with hair, and projecting considerably beyond the short under-jaw, 
are well-known characters of the Rodentia, which are not common to the 
Saltigrade Marsupials; in which, more especially among the smaller sized 
species, the head is attenuated and flattened sideways, the extremity of the 
muzzle naked, and the under-jaw nearly of the same length as the upper. 
Secondly, the character of the tail, naked and scaly throughout the greater 
part of its length, and terminated by a large pencil of long hair, is unknown 
among the Saltigrade Marsupials, and universal among the Jerboas. "Thirdly, 
the three middle toes of the hind feet are of the same size, and originate on 
the same line, a strueture likewise characteristic of the Jerboas, whilst the 
Saltigrade Marsupials, on the contrary, have the lateral toes placed consider- 
ably behind the middle, and of much smaller size. Fourthly, there is no 
known instance of a Saltigrade Marsupial with an additional or accessory toe, 
placed half-way up the tarsus, as represented in the figure of Dipus Mitchellii, 
though the character is common enough among the Jerboas ; and lastly, there 
is no known instance of a Saltigrade Marsupial which has not the two internal 
toes of the hind feet united, or of a Rodent that has. In this last chai 'acter, as 
in all the rest, the drawing of Dipus Mitchellii perfectly agrees with the true 
Jerboas, and differs from the Saltigrade Marsupials ; so that if it eventually turn 
out to belong to this latter family, it must possess the characters of an essen- 
tially new form, of a genus no less singular than novel. It may be observed, 
in conclusion, that the fidelity of the figure is unquestionable ; Major Mitchell 
is well known to be a skilful draughtsman ; he made his sketch upon the spot 
when the animal was captured ; and not being himself a zoologist, it is utterly 
impossible that he could have so accurately depicted the characters of the 
genus Dipus, of which he had perhaps never heard, had he not drawn from 
the model. 
