44 
ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
beneath is covered with minute silvery- white hairs ; beside the ordinary 
tubercles, the anterior portion of the sole of the foot and the base of the toes 
beneath, are crowded with small rounded warts, which are much more nume- 
rous and conspicuous than in the common mouse. 
Length from nose to root of tail 
of tail .... 
from nose to eye 
In. Lines. 
. 3 1 
. 1 11 
• 0 
Length from nose to base of ear 
of tarsus (claws included) . 
of ear 
In. Lines. 
0 8f 
0 S 
0 4 ^ 
Habitat, Maldonado, La Plata, {June.) 
The skull of this animal, is rather shorter and broader than that of Mus 
Musculus, the upper surface is more arched, the zygomatic arch is much more 
slender, and the nasal bones are rather broader. In the convexity of the upper 
surface, and the slenderness of the zygomatic arch, this skull very nearly resem- 
bles that of M. gracilipes ; this latter, however, has the zygomatic arch more 
convex, projecting more suddenly on the anterior part, and the interparietal bone 
smaller. Length of skull 10 lines, width 5^, length of nasal bones 4 lines, 
distance between the outer side of the incisors, of the upper jaw, and the first 
molar lines. See Plate 34, fig. 3. a. 
The dentition is figured in Plate 34, figs. 3. b and c. 
This mouse is rather less than M. Musculus, the tail is much shorter in pro- 
portion, the fur is longer and softer, and the ears are more distinctly clothed with 
hair. 
The pale and delicate yellow colour of the upper parts of the body, and the 
pure white of the under parts, renders the present species conspicuous amongst 
its congeners. I may further remark that the white colour which in the Muridse 
(when it occurs) is usually confined to the under part of the body, or extends 
but slightly on the sides, is in the present animal extended considerably on 
the sides of the body, and occupies an equal portion with the yellow of the upper 
parts. The name bimaculatus is applied to this animal on account of the two 
conspicuous white patches, which are situated behind the ears. 
In affinity as well as in appearance it most nearly approaches to Mus 
gracilipes and M. elegans ; with no other species of the genus Mus, here described, 
can it be confounded, since these only have the tarsus hairy beneath. 
The principal points of distinction between the present animal and Mus 
elegans , are noticed in the account of that species. 
“ This mouse, when alive, had a very elegant appearance. A countryman, 
who brought it me, found six of them living together in one burrow.” — D. 
