This species is rather larger than the common mouse; its head is
proportionately larger, the ears are smaller, the tail considerably
shorter, and the fur longer, and in colouring it is a little darker. In
size and colour it resembles _M. Magellanicus_, but the shorter tail and
tarsi, and the smaller size of the ears will serve to distinguish it.
The skull of _Mus arenicola_, Plate 34. fig. 7, _a_, is rather larger
than that of _Mus Musculus_, the nasal portion is broader, the
interparietal bone is much smaller, especially in antero-posterior
extent; the zygomatic arches are more slender, and the incisive foramina
are broader. The horizontal ramus of the lower jaw (Pl. 34. fig. 7,
_d._) is rather less curved, the coronoid process is more elongated, and
the condyloid is narrower and also larger. The length of the skull is 11
lines and a half; the width is 6½ lines. The molars of the upper jaw are
figured in plate 34 fig. 7, _b._ and those of the under jaw, fig. 7,
_c_.
“This specimen was caught on the open grassy plain, by a trap baited
with a piece of bird; it is, however, very abundant in the sand hillocks
near the coast of the Plata.”—D.
13. MUS BRACHIOTIS.
PLATE XIV.
Mus brachiotis, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 17.
_M. suprà obscurè fuscus, subtùs obscurè griseo tinctus; pedibus
griseo-fuscis; auribus parvulis; caudâ quoad longitudinem, corpus
ferè æquante: vellere longo et molli._
DESCRIPTION.—Fur soft, very long, and dense; ears very small; general
colour brown: the hairs of the upper parts, and sides of the head
and body are of a deep gray at the base, black at the apex, and
narrowly annulated with deep yellow near the apex; on the throat
and belly they are of a paler gray at the base, and grayish white
at the apex. The ears are well clothed with brown hairs both
within and without, and are for the most part hidden by the long
fur of the head. The hairs covering the upper side of the feet are
of a palish ashy-brown colour, and the fleshy portion appears to
have been brown. The tail is well clothed with hairs, so that the
scales are scarcely visible; on the upper side of the tail the
hairs are brownish black, and on the under side, they are dirty
white. The incisors are very slender; those of the upper jaw are
of a very pale yellow colour, and those of the lower are white, or
nearly so. The muzzle is slender, and pointed.
In. Lines.
Length from nose to root of tail 4 9
of tail 2 8
from nose to base of ears 1 2
of tarsus (claws included) 0 11
of ear 0 3