GERBILLUS TENUIS. 
those of the upper, laterally compressed, and sharp at the point. The molars 
of the upper jaw are constructed much like those of the last species, and each 
consists of the same number of divisions, the second and third divisions 
of the front tooth differ however a little in configuration, the sides of 
the tubes being so compressed as to give the surface of the crown of each 
division more or less of the form of the figure 8. The front molar of the 
lower jaw is triangular anteriorly, and composed of two distinct portions, the 
anterior of which is again sub-divided into two, so that, when the tooth is 
viewed laterally, it exhibits an appearance of three divisions ; the central con- 
cavity of the anterior division, which consists of the two sub-divisions, 
resembles somewhat the figure of a club, as painted upon playing cards ; the 
cavity of the second division is narrow and nearly of equal width throughout ; 
the second tooth consists of two transverse portions in close approximation to 
each other, and the third of one with its centre concave. The nasal bones 
are 5^ lines in length ; the distance between the hinder edge of the incisors 
of the upper jaw and the anterior surface of the first molar, where it is in 
contact with the alveolar processes, 3| lines ; length of the row of molar teeth 
2j lines. Zigomatic arch anteriorly flat, thin, and moderately broad, pos- 
teriorly narrow, slender and very delicate. For representations of the teeth, 
&c., see Plate XXXVII. 
This species was first found after the expedition passed to the northward of Latakoo, and 
although a number of individuals were seen from time to time, yet only three were captured. 
It inhabits open localities, similar to those resorted to by the species already described, and, 
according to the statements of the natives, its habits resemble those of G. Afer. 
Its size and slender form at once bespeak it as a distinct species, and its anatomical charac- 
ters lead us to regard it as more allied to G. Afer than to any of the other South African 
species with which we are yet acquainted. 
