The molars of the upper jaw are figured in Plate 34, fig. 15, _a_, and
those of the lower jaw, fig. 15, _b_.
“Inhabits the dry gravelly plain, bordering the Rio Negro.”—D.
24. MUS XANTHOPYGUS.
PLATE XXII.
Mus xanthopygus, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 28.
_M. suprà pallidè brunneus flavo-lavatus, ad latera flavescens, subtùs
albus; capite griscescente; natibus flavis; pedibus albis; auribus
majusculis pilis, albis et flavis intermixtis obsitis; caudâ quoad
longitudinem, corpus ferè æquante, suprà nigricante, subtùs albâ;
vellere longo et molli; mystacibus perlongis albescentibus, ad basin
nigris._
DESCRIPTION.—Ears rather large, tail rather longer than the body,
tarsi moderately long and somewhat slender: fur long and very
soft: prevailing tint pale yellow; on the back there is a brownish
hue owing to the long hairs, which are thickly interspersed with
ordinary fur, being of that colour: in the region of the tail the
hairs are of a rich yellow colour; the tip of the muzzle is white,
the feet, chin, throat and the whole under parts of the body are
white; on the chest and belly a faint yellowish hue is observable:
the tail is well clothed with tolerably long hairs, those on the
apical portion are the longer, on the upper side of the tail they
are of a brown colour, and on the under side they are pure white:
the ears are well clothed with tolerably long hairs, those on the
inner side are of a pale yellowish colour, externally on the fore
part they are brown, and on the hinder part they are yellowish
white: the hairs of the moustaches are numerous and very long;
some of them are white, but the greater portion are brownish black
at the base and whitish at the apex: the upper incisors are
yellow, and the lower are yellow-white: the hairs of the ordinary
fur on the back are gray at the base, brownish at the tip, and
very pale yellow near the tip: the hairs on the belly are gray at
the base and white externally.
In. Lines.
Length from nose to root of tail 5 3
of tail 3 10
from nose to ear 1 3
of tarsus (claws included) 1 1
of ear 0 7
There are three specimens of the present species in Mr. Darwin’s
collection; two of them were caught when shedding their fur, and having
lost the longer black hairs, have the upper parts of the body of a paler
colour; their general tint is very pale, and may be described as gray,
with a wash of pale yellow.
This species is closely allied to the last, but differs in being rather
smaller, in having smaller ears which are well clothed with hair, and
not sparingly furnished as in _Mus griseo-flavus_, and in having a
shorter tail which, like the ears, is more densely clothed with hairs;
in the structure of the molar teeth there also differences which will be
better understood by comparing the drawings. Fig. 16, _a_, Plate 34,
represents the molars of the upper jaw, and 16, _b_, those of the lower
jaw.
“Extremely abundant in the coarse grass and thickets in the ravines at
Port Desire and Santa Cruz: was caught in a trap baited with cheese.”—D.
25. MUS DARWINII.
PLATE XXIII.
Mus Darwinii, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 28.
_M. suprà pilis pallidè cinnamomeis et nigrescentibus intermixtis;
ante oculos cinerascentibus; genis, lateribus corporis, et caudâ
prope basin, pallidè cinnamomeis; partibus inferioribus pedibusque
albis; auribus permagnis; caudâ caput corpusque ferè æquante, suprà
fusco-nigricante, subtùs albâ._
DESCRIPTION.—Form robust; ears immensely large; tail nearly equal in
length to the head and body taken together; fore feet very small;
tarsi moderate; fur very long and soft; general tint of the upper
parts pale cinnamon yellow; on the rump a richer yellow hue
prevails, and on the back there is a brownish tint, owing to the
interspersed long hairs being of that colour; the upper surface of
the head is grayish; the cheeks, like the sides of the body, are
of a delicate yellow colour, faintly clouded with brown; the sides
of the muzzle, lower part of the cheeks and sides of the body, and
the whole under parts, are pure white; the feet and tail are also
white, if we except the upper surface of the latter, which is dark
brown; the yellow tint of the sides of the body is extended
downwards on the outer side of the fore legs and on the back of
the hinder legs; the ears are but sparingly furnished with hair,
excepting on the fore part, externally, where they are of a
brownish colour; the minute hairs which cover the remaining parts
of the ear are very pale; the tail is well clothed with hairs; the
hairs of the moustaches are numerous and very long; they are for
the most part blackish at the base, and gray at the apex; the
incisors are rather slender, the upper pair are an orange colour,
and the lower, yellow; the hairs of the ordinary fur of the back
are gray at the base, broadly annulated with pale cinnamon yellow
near the apex, and brownish at the apex; the hairs of the belly
are deep gray at the base, and white externally, those on the
throat are pale gray at the base.
In. Lines.
Length from nose to root of tail 6 0
of tail 4 9
from nose to ear 1 4½
of tarsus (claws included) 1 1½
of ear 0 11¾
Width of ear 1 0½[24]