SCIETOMTS TETRADACTYLUS. 
311 
SCIRTOMYS. 
Scirtomys, Brandt^ Bull. Ac. St. Petersb. ii. 1844, p. 220 . 
Four toes on the hind feet. 
Dentition : i. j, pm. g, m. g = 18. 
Incisors without grooves. 
Scirtomys tetradactylus, Licht. 
Bipus tetradactylus, Licht. Verz. Doubl. Berlin, 1823, p. 2; id. Abb. k. Akad. Wissensch. Berl. 
1825 (1828), p. 153, tab. hi. •, id. Barst. 1827, tab. xxiii. fig. inf. 
Scirtomys tetradactylus, Brandt, Bull. Acad. St. Petersb. ii. 1844, p. 220. 
Lichtenstein indicated a species of jumping desert-rat which he designated Di^us 
tetradactylus, “ e deserto Lihyco inter Sivam et Alexandriam.” 
The unique example of this species is preserved in the Berlin Museum, and I am 
indebted to Mr. Matschie for having been permitted to examine it. 
This animal is intermediate in size between Jaculus jaculus and J. orientalis, with 
long pointed ears; they are longer, more pointed, and narrower even than in J. orientalis. 
It is coloured much the same as the latter. The tail seems to be relatively shorter 
than in either of these species, but is marked the same way at the extremity. The 
first or inner toe is entirely wanting, as in Jaculus, but in Scirtomys the outer or fifth 
toe is found, though quite functionless, on the outer side of the tarsus, considerably 
removed from the other toes. 
Snout to vent.218 
Vent to tip of tail.250 
Height of ear. 32 5 
Breadth of ear, approximate. 25 
Length of tarsus. 57 
Distance of origin of fifth toe above extremity of middle toe. 31-8 
Length of fifth toe, without claw. 7 
The upper incisors are perfectly smooth. In Scirtomys, besides three upper molars, 
there is a premolar, absent in Dipus: this tooth is very small, unicuspidate, and 
conical. 
The preorbital prolongation of the malar is very feeble, as also is the process of the 
maxillary, so that the exterior boundary of the preorbital foramen is reduced to little 
more than a vertical rod, these parts in Jaculus forming a broad widely projecting 
plate. The interorbital region compared with that of Jaculus is somewhat narrow. 
