Upon comparing the skull (Pl. 34, fig. 2, _a._) of _M. elegans_ with
that of _M. Musculus_, the most evident points of distinction consist in
the greater proportionate length of the nasal and frontal bones, and the
slenderness of the zygomatic arch in the former animal. Length of skull
11 lines, width 6 lines, distance between front molar and outer side of
incisors of upper jaw 3⅜ lines, length of nasal bones 4⅜ lines.
The dentition is figured in Pl. 34, figs. 2. _b_, and 2. _c_.
“Whilst bivouacking one night on shore, amongst some sand hillocks, this
mouse, with its tail singed, leapt out of a bush which was placed on the
fire. Its hind legs appeared long in proportion to the front, and it did
not appear to be very active in endeavouring to make its escape.”—D.
_Mus elegans_ is about equal in size to _M. Musculus_; the head is
larger in proportion than in the latter, the ears are slightly larger,
the tail is longer, and so are the tarsi. The large ears, long tail, and
comparatively large size of the feet, combined with the greater size of
the animal itself, will render it easy to distinguish this species from
_M. gracilipes_ and _M. bimaculatus_. From the last mentioned animal it
moreover differs in having the head larger in proportion, the fur
longer, and the colouring of the upper parts of the body somewhat
darker. The white fur is almost confined to the under parts of the body,
and there is but a small tuft of white hairs behind the ears, whereas in
_M. bimaculatus_, the white fur extends considerably on the sides of the
body, the outer side of the limbs are white, and there is a large and
conspicuous white spot behind each ear.
In _M. elegans_ the whole sole of the tarsus and the carpal tubercles
are covered with hair. In _Mus bimaculatus_ the hinder _half_ of the
tarsus only is covered with hair, and in _M. gracilipes_ both the hinder
half is covered, and there are some scattered hairs extending almost to
the two tubercles, which are situated at the base of the longer toes.
The genus _Eligmodontia_ of M. F. Cuvier, founded upon a species of
mouse from Buenos Ayres, possesses nearly the same characters as the
subgenus _Calomys_, established by me in the Proceedings of the
Zoological Society for February 1837, and which included the animal
above described, and two other species (_M. bimaculatus_ and _M.
gracilipes_). M. Cuvier’s genus is distinguished by there being only one
large tubercle on the under side of the tarsus, and in having the carpal
pad covered with hair as well as the pad of the tarsus. In these
characters our present animal agrees, as it does also in size and in the
relative proportions of the tail and tarsus, circumstances which induce
me to believe they are identical.
In _M. bimaculatus_ and _M. gracilipes_ there are six naked tubercles on
the under side of the tarsus, and the carpal pad is also naked. In
having, however, the tarsus hairy beneath,[20] in dentition and in
colouring, they agree so closely with _M. elegans_ that I think they
cannot be separated generically.
MUS BIMACULATUS.
PLATE XII.
Mus bimaculatus, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 18.
_M. vellere pallidè ochraceo, pilis nigricantibus adsperso, his ad
latera rarioribus; rostri lateribus, notá magná pone aurem utramque,
artubus, corporeque subtùs niveis; auribus mediocribus; caudâ, quoad
longitudinem, corpus fere æquante; tarsis ad calcem pilis
argenteo-candidis obsitis._
DESCRIPTION.—Upper parts of the body of a very pale ochre colour, the
longer hairs, however, are black, and at the apex grayish, and
where they are numerous, as on the back and upper surface of the
head, they give greater depth to the colouring; the cheeks and
sides of the body are of an almost uniform pale, but bright
yellow; the sides of the muzzle, the lower half of the cheeks, the
lower portion also of the sides of the body, and the whole of the
under parts, are pure white—each hair being uniform in colour to
the root, and not, as is usually the case, _gray_ at the root.
There is likewise a large patch of pure white hairs behind each
ear. The feet and tail are of a pale flesh-colour, and furnished
with white hairs, with the exception of those on the upper surface
of the latter, which are pale brown. The ears are also pale
flesh-colour, clothed internally with yellow hairs; externally on
the fore part, the hairs are brownish, and on the hinder part,
white—they are rather large, and so are the feet. The tail is
about equal to the body in length. The hairs of the moustaches are
numerous and slender, and most of them are black at the base, and
gray at the apex. The hinder half of the tarsus beneath is covered
with minute silvery-white hairs; beside the ordinary tubercles,
the anterior portion of the sole of the foot and the base of the
toes beneath, are crowded with small rounded warts, which are much
more numerous and conspicuous than in the common mouse.
In. Lines.
Length from nose to root of tail 3 1
of tail 1 11
from nose to eye 0 4½
from nose to base of ear 0 8¾
of tarsus (claws included) 0 8
of ear 0 4½