| OCR Text |
Show 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, which are marked with parallel constrictions. 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 oi 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 bulla? 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 zvgoma 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 tbe 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 Bipus, 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 prolongation of tbe nasal cavity formed by the nasals and premaxilla?, the opening of which is considerably in front of the anterior line of the incisors, while the reverse is the case in 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. |
