58 SKETCH OF THE HISTORY OF MAMMALIA. 



Darwin's Mouse (Mus Darwimi). 



Among the numerous small Rodents belonging- to the 

 family MuridcB collected by Mr, Darwin (see ' Zool. of 

 H.M.S, Beagle '), is a small group, the species of 

 which, Mr. Waterhouse observes, though very closely 

 allied to the genus Mus^ offer some slight modification 

 not only in their external form, but also in the structure 

 of the teeth. 



''They have the fur soft and silky; the head large; 

 and the fore-legs very small and delicate ; the tarsus 

 moderately long, and bare beneath. In the number and 

 proportion of their toes they agree with the true rats ; 

 the tail is moderately long and more thickly clothed with 

 hair than in the typical rats. The ears are large and 

 clothed with hair. Like the true rats, they have twelve 

 rooted molars; the folds of enamel, however, penetrate 

 more deeply into the body of each tooth, and enter in 

 such a way that the crowns of the teeth are divided into 

 transvei'se and somewhat lozenge-shaped lobes of a tri- 

 angular form. In the front molar of the upper jaw the 

 enamel enters the body of the tooth twice, both in the 

 outer and inner sides ; and in the second and posterior 

 molars, both of the upper and under jaws, the enamel 

 penetrates but once externally and internally in each. 

 In the front molar of the lower jaw the enamel enters 

 the body of the tooth three times internally and twice 

 externally" (' Proc. Zool. Soc.,' 1837, p. 27). These 

 murine animals Mr. Waterhouse regards as constituting 

 a subgenus, for which he proposes the name of Phijllotis. 

 Darwin's mouse, Mus (^Phyllotis) Darwinii, was found 

 in dry and stony places at Coquimbo in Chile. The fur 

 above consists of cinnamon-coloured and blackish hairs 

 intermixed ; the space before the eyes is of a grayish 

 tint ; the sides of the face and body are of a pale cin- 

 namon colour. The under parts and limbs white; the 

 ears are large ; the tail as long as the head and body, 

 brownish above, white beneath. Length of head and 

 body six inches. (Fig. 35.) 



Besides the subgenus Phyllotis, Mr. Waterhouse cha- 



