1890.] 



MR. W. L. SCLATER ON A NEW JERBOA. 



611 



in length between these toes is very much greater in A. indica and 

 in all other species of Alactaga that I have been able to examine. 



Beneath the three median toes of all Jerboas there are large 

 laterally compressed pads, wbich are marked with parallel con- 

 strictions. In Euchoreutes there are four constrictions on each 

 toe-pad, while in Alactaga there are four constrictions on the median 

 toe and only three on the second and fourth toes. 



The tail resembles that of Alactaga ; it is very long and tufted, 

 with long hairs at the end ; the tuft is basally white, but black in 

 the middle and white again at the tip. The hairs of the tuft are 

 equally developed all round, and do not seem to be arranged in so 

 distichous a manner as in Alactaga. 



Skull of Euchoreutes naso. 



The skull o^ Euchoreutes is of a much longer and more slender 

 type than that of any other species of Jerboa, and is altogether very 

 distinct in general appearance. 



The nasals are very long and narrow and the bullae much inflated, 

 so that when the skull is viewed from above they project both 

 laterally and posteriorly, and give it a very different appearance from 

 that of all other Jerboas. There is also a very marked constriction 

 of the frontal bones in the middle of their length just above the eye; 

 this is quite unrepresented in the skull of Alactaga. 



The zygoma is very weak and thin, and the vertical portion, 

 which separates the optic from the antorbital foramen, is also very 

 thin, and slopes from above downwards posteriorly, while in Alactaga 

 the corresponding part of the zygoma is either vertical or anteriorly 

 directed ; in consequence of this the antorbital foramen is very 

 differently shaped, being about half the size of the optic foramen ; 

 there is, as in Dipus, a separate canal at the base of the foramen for 

 the exit of the nerve. 



Another very distinctive feature of the skull of Euchoreutes, 

 when viewed laterally, is the long anterior trumpet-shaped pro- 

 longation of the nasal cavity formed by the nasals and premaxillse, 

 the opening of which is considerably in front of the anterior line of 

 the incisors, while the reverse is the case iu all the other skulls of 

 Jerboas which I have been able to examine. 



Viewed from below, the anterior palatine foramina will be seen to 

 be very large and to extend back to behind the anterior line of the 

 molars, while in Alactaga they do not extend so far as the anterior 

 line of the premolars. 



