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 







4^ 



Length from nose to base of ear 



of tarsus (claws included) 



of ear 



In. 



Lines. 







8f 







8 







4.4 



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 5J, 



length of nasal bones 4 lines, 



distance between the outer side of the incisors, of the upper jaw, and the first 



molar 2| 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 31. 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 Muridae 

 (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 

 vracilipes and 31. 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. 



ct 



