150 CLASS MAMMALIA. 



a thumb scarcely apparent on the fore-paws, with a very 

 short nail. Five on the hinder. 



The upper part of the body is a pale gray-fawn, varied 

 with brown. The under is white, and the buttocks are 

 marked, as in the two preceding species, with a white 

 transversal band. The muzzle is white at the extremity, 

 and brown above, like the Alactaga, and not the same 

 colour as the back, like the Little Gerboa. 



This variety is greatly multiplied. It is found especially 

 in Oriental Tartary, and Siberia. Beyond the lake Baikal, 

 it is the only variety found, and probably in the deserts of 

 Mongolia. 



The last variety of the Mus Jaculus of Pallas is the Little 

 Gerboa, or Dipus Minutus of M. de Blainville. It differs 

 from the first in the proportions of various parts, and in its 

 little tail, which does not exceed that of the Mulot. The 

 difference of size does not depend on age, inasmuch as the 

 individuals of this small variety have the epiphyses of the 

 bones as completely consolidated as those of the Alactaga 

 and Gerboa Brachyura. 



There are four toes, and a small thumb on the fore-paws, 

 and five on the hinder. The hinder extremities and tail are 

 proportionally longer than in the last variety. The jaws 

 on each side have one molar less than in the Alactaga and 

 Gerboa Brachyura. The thigh-bone, which in the Alactaga 

 is as long as two-thirds of the tibia, is here longer than the 

 tibia. The hairs of the tail are ranged like the barb of a 

 quill, an arrangement less apparent in the preceding species, 

 and the white part of the tuft is less extended. 



All the upper part of the body is a yellowish-gray mixed 

 with brown. The under part is a beautiful white, as also 

 are the paws and feet. There is on each side of the buttocks 

 a white transversal band, slightly crescented. The principal 

 characteristic of this variety is, that the muzzle instead of 

 being white is the same colour as the upper part of the 



