This species is nearly equal in size to the common rat (_Mus
decumanus_). Of its skull[23] I possess but the anterior portion (see
Pl. 33. fig. 3, _a._ and 3, _b._): it appears to have been about the
same size as that of _M. decumanus_, its proportions, however, are
different: the nasal portion is broader and shorter, the ant-orbital
outlet is rather smaller; the plate, forming the anterior root of the
zygomatic arch, and which protects this outlet, has its anterior edge
distinctly emarginated, and not nearly straight as in _M.
decumanus_,—the zygomatic arch is stouter, the space between the orbits
is narrower, the palate is more contracted, the incisors are much
broader, less deep from front to back, and have the anterior surface
more convex; the molar teeth are larger; the lower jaw (see Plate 34.
fig. 12, _a._) when compared with that of _Mus decumanus_ also offers
many points of dissimilarity; the principal differences consist in its
greater strength, the comparatively large size and breadth of the
articular surface of the condyles, the upright position of the coronoid
process—a perpendicular line dropt from the apex of which would touch
the posterior part of the last molar—and the great extent of the
_symphysis menti_. In the form of the incisors, the more contracted
palate, the great extent of the _symphysis menti_, and in fact in most
of the points of dissimilarity, between the skull of the present animal
and that of _Mus decumanus_, here pointed out, it will be perceived,
there is an approach made to the _Arvicolidæ_.
The dimensions of the skull (so far as an imperfect specimen will allow
of their being taken) are as follows:—
In. Lines.
Distance between front of incisors, (upper jaw) and the
first molar tooth 0 8
Longitudinal extent of the three molars on either side,
taken together 0 4¼
Length of nasal bones 0 7¼
—— of incisive _foramina_ 0 4¼
Width between orbits 0 2½
Length of _ramus_ of lower jaw 1 1¼
Fig. 3, _c_, Plate 33, represents the molar teeth of the upper jaw. Fig.
3, _d_, those of the upper jaw.
“This rat was caught at Bahia Blanca where the plains of Patagonia begin
to blend into the more fertile region of the Pampas. It lived in holes
amongst the tussocks of rushes, on the borders of a small, still, brook;
in its manner of diving and aquatic habits it closely resembled the
English water-rat, (_Arvicola amphibia_.)”—D.
When at Paris I examined what I believe to be the original _Mus
Braziliensis_, since the specimen was labelled “_Rat de Brazil St.
Hilaire, 1818_.” It agrees perfectly with the present animal excepting
in being rather smaller, the length from the nose to the tail being 7
inches and 4 lines—the length of the tail is 7 inches 9 lines, and that
of the tarsus is 1 inch 11 lines; this difference in the length of the
body may arise from difference of age, or even of sex. In the Paris
Museum I saw what appeared to me to be a variety of the same species in
which the under parts of the body are white.
I have been minute in my description of the _Mus Braziliensis_, since it
is confounded by Desmarest, Fischer and Lesson with the _Rat troisieme_
or _Rat Angouya_ of Azara, which I believe to be a very different
animal. The description given by the authors just mentioned are taken
from Azara, who gives the following characters to distinguish the _Rat
Angouya_: “Du museau à la queue, et sur les côtés du corps tout est
brun-cannelle, parceque les poils ont une petite pointe cannelle; puis,
ils sont obscurs et enfin blanc vers las peau. Toute la partie
inférieure de l’animal est blanchâtre, plus claire sous la tête, et plus
foncée entre les jambes de devant; le pelage est doux, très-serr, et le
poil, qui est à la racine de l’oreille, cache le conduit de celle-ci.”
In. Lines.
Length from nose to root of tail (English measure) 6 0
of tail 6 6½
of ears 0 9¾
of tarsus (the claws included) 1 3¼
It appears from this description that the _Mus Angouya_ is a smaller
animal, and differs both in colouring and proportions from the _Mus
Braziliensis_. Brandt has figured and described a rat under the name of
_Mus Angouya_, which in many respects agrees better with Azara’s
description; there are, however, discrepancies in the dimensions.
22. MUS MICROPUS.
PLATE XX.
Mus micropus, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 17.
_M. suprà fuscus; subtùs cinerescenti-albus, pallidè flavo tinctus;
pedibus pilis sordidè albis tectis, antipedibus parvulis; auribus
parvulis; caudâ, quoad longitudinem, corpus ferè æquante, suprâ
fuscâ, subtùs sordidè albâ._
DESCRIPTION.—Form stout, ears rather small, tail nearly equal to the
body in length, fur very long and moderately soft, general colour
of the upper parts of head and body, brown; of the sides of the
body grayish, faintly washed with yellow, of the under parts
grayish white, faintly tinted with yellow; hair covering the upper
surface of the feet dirty white; on the tarsus there is a very
slight yellow tint; ears well clothed with hairs, those on the
inner side chiefly of a yellow colour; tail above, dusky brown;
beneath dirty white: hairs of moustaches black at the base and
grayish at the apex; incisors pale yellow: hairs of the back deep
gray at the base, annulated with brownish yellow near the apex,
and dusky at the apex; longer hairs dusky black; hairs of the
belly deep gray at the base and broadly tipped with yellowish
white.
In. Lines.
Length from nose to root of tail 6 0
of tail 3 8
from nose to ear 1 4
of tarsus (claws included) 1 0¾
of ear 0 6