tudinal groove along its centre; those of the lower jaw long, slender, and
plain. The molars are six in each jaw, three on each side, the front one of
upper jaw is largest, and its crown consists of three transverse divisions, each
division a sort of tube, the anterior and posterior sides of which are nearly in
contact, and only connected with the adjoining division at a point about equidistant
between their inner and outer sides; the second and third teeth consist
of two divisions constituted in the same manner as the first, the last division
of the third tooth being very small and subtriangular. The molars of the lower
jaw are similarly constructed. Length of the ossa nasi 7 lines; distance between
incisors of upper jaw and base of first molar lines ; length of the row of
molars 2§ lines. For representations of the Teeth, &c., see Plate XXXVII.
This species inhabits the summit of hills in the country to the north of the Orange River
towards its sources, and is generally found in situations devoid of shrubs, where the grass is
short. Its principal operations are carried on during the night, and under the cover of darkness
it seeks its food, forms its burrows, and changes its residence.
The incisor teeth o f the upper jaw are much larger in this species than in Gerbillus Afer,
and the distance between the incisors and first molar is less; hence the muzzle is considerably
shorter, and consequently, the head appears more clumsy: there is also a difference as regards
the fur; it is more closely set and better adapted to protect against the greater cold to which
it is necessarily exposed. The nails of the fore feet also furnish diagnostic characters of the
animal, as will be seen by comparing the descriptions o f those organs in the two species; the
nails of G. montanus are vertically more compressed and like those of G. tenuis.
GERBILLUS TENUIS.- S m it h .
Mammalia.—P late XXXVI. Fig. 2.
G. capite, dorso, lateribus, extremitatibusque extemè pallide rubro-aurantiis, dorso brunneo-
penicillato ; partibus inferio.ribus extremitatibusque interné versus corpus albis ; oculis r ubro-
brunneis.
Longitudo ab apice nasi ad basin caudee 4 une. ; caudæ 4£ une.
CoLouiiE-The head, the hack, the sides, and the outer surface of the
extremities a clear pale reddish orange ; the back freely pencilled with liver-
brown ; the hairs towards their root dull lavender-purple ; chin, throat, belly,
and inner surface of limbs pure white ; tarsi pale ochrey white. The line of
demarcation between the colours of the sides and belly distinctly defined.
Tail the same colour as the back, only lighter, and towards its point many
of the hairs are of an umber-brown tint. Ears internally a pale flesh
colour, externally, pale yellowish brown. Eyes deep reddish brown. Claws
pale wood-brown. Incisor teeth of upper jaw pale Dutch-orange, of lower
jaw pale straw-yellow.
F o r m , & c .—Figure slender and moderately lengthened ; head rather small
and anteriorly attenuated ; the apex of the nose rather acute. Eyes large ;
ears moderately long and oval : whiskers very long, and towards their origin,
rigid. Hair of the muzzle short and rather strong, that covering the rest of
the head, the body, and the extremities, as far as the tarsi, long, soft, silky,
and recumbent. The hair disposed along the centre of the back not quite
so soft as the rest ; hair of tarsi and toes very short and rigid. Tail slender,
cylindrical, and tapering, the hair dense, rigid, and very short, except at the
point, where it is lengthened and forms a thin tuft. Fore-legs short, hinder
legs long ; toes moderate ; nails pointed, vertically compressed, slightly arched,
and those of the fore-feet longest.
Teeth, & c .—Incisors of upper jaw incurved, moderately strong, and with
sharp-cutting points : they protrude about a line-and-a-half beyond the alveoli,
and each, anteriorly along its middle, is marked with a deep longitudinal
furrow; the incisors of the lower jaw are slender, considerably longer than