Chapter III: Part 3

These two animals not only differ in the colour of the fur, one being of a grizzled brownish colour, and the other black, but there is a considerable difference in the texture of the fur. In the black specimen, the fur is very soft and glossy, and the long hairs, which are abundant, are very slender. In the brown specimen, the fur is of a harsher nature, the long hairs are not so abundant, but longer, and less slender. On the other hand, they agree in size, dentition, the length of the head, tarsus, and ears, and differ but in a trifling degree (about three lines,) in the length of the tail.

Upon comparing the Ascension Island specimens with _M. Rattus_, I find that, although in size they are about one-third less, yet the teeth precisely agree, not only in form, but in size. The relative proportions of the head, ears, and tarsi, also agree. Besides the general colouring of the fur, they both differ in having the hairs of the feet uniformly purple-black, those in _Mus Rattus_ being much paler, and even whitish, on the toes. In the character of the fur, there is much difference. The long silky hairs, which are so conspicuous in _Mus Rattus_, are replaced, in the black specimen, by hairs which are scarcely to be distinguished from the ordinary fur; and in the other specimen, although rather longer and more distinct, they are short, compared with those of the black rat.

“The specimen which has a black, and glossy fur, frequents the short coarse grass near the summit of the island, where the common mouse likewise occurs. It is often seen running about by day, and was found in numbers, when the island was first colonized by the English, a few years since. The other, and browner coloured variety, lives in the out-houses near the sea-beach, and feeds chiefly on the offal of the turtles, slaughtered for the daily food of the inhabitants. If the settlement were destroyed, I feel no doubt that this latter variety would be compelled to migrate from the coast. Did it originally descend from the summit? and, in the case just supposed, would it retreat there? and, if so, would its black colour return? It must, however, be observed, that the two localities are separated from each other by a space, some miles in width, of bare lava and ashes. Does the summit of Ascension, an island so immensely remote from any continent, and the summit itself surrounded by a broad fringe of desert volcanic soil, possess a small quadruped, peculiar to itself? Or, more probably, has this new species been brought, by some ship, from some unknown quarter of the world? Or, I am again tempted to ask, as I did in the case of the Galapagos rat, has the common English species been changed, by its new habitation, into a strongly marked variety?”—D.

Mr. Darwin seems to have foreseen the difficult problem which these two rats have furnished, and although I have spent much time in studying the Muridæ, I must confess I have been exceedingly puzzled by the animals in question. It appears as if the brown, and black rats, (_M. decumanus_, and _M. Rattus_,) and likewise the common mouse, (_M. Musculus_,)[16] all of which follow man in his peregrinations, and which, to a certain degree, are dependent upon man, and may therefore be termed semi-domestic animals; like _really_ domestic animals, are subject to a greater degree of variation than those species which hold themselves aloof from him.

Upon the whole then I have determined to describe the two Ascension Island specimens as one species, and as varieties of the _Mus Rattus_, but with a mark of doubt, since I do not possess sufficient materials for a rigorous examination, having, in fact, but one skin of each variety, and neither skull nor skeleton. I have also applied the name of _insularis_, to designate this variety or species, whichever it may be, for, supposing it be not a distinct species, it is so marked a variety, that a name for it is desirable.

5. MUS MUSCULUS.

Mus Musculus, _Auctorum_.

Of this species, there are six specimens in Mr. Darwin’s collection; two were found “living in the short grass, near the summit of the Island of Ascension, where the climate is temperate.”—D. Two others were procured “on a small, stony, and arid island, near Porto Praya, the capital of St. Jago, in the Cape de Verde Islands,—climate very hot and dry. Excepting during the rainy season, which is of short duration, these little animals can never taste fresh water, nor does the island afford any succulent plant.”—D. A specimen was also procured “on a grassy cliff, on East Falkland Island, at the distance of a mile from any habitation. It is singular that so delicate an animal should be able to subsist under the cold, and extremely humid climate, of the Falkland Islands, and on its unproductive soil.”—D. These specimens are all of them rather less than full grown individuals of the same species procured in England; in other respects, they do not differ.

The sixth specimen, which is from Maldonado, is considerably less than British specimens of the common mouse, and is of a richer and brighter colour, the head is smaller, the muzzle shorter in proportion, whilst the tarsi are even longer than in a large specimen of _M. Musculus_. These points of dissimilarity induced me to believe it was a distinct species, and to apply to it the specific name of _brevirostris_.[17] Upon re-examination, with the advantage of more experience, and consequently a better knowledge of the characters of these animals, I have changed my opinion. The teeth indicate that it is not an adult specimen, and agree perfectly with those of _M. Musculus_, both in form and size. “Common in the houses of the town of Maldonado, and its habits are similar to those of _Mus Musculus_.”—D.

6. MUS LONGICAUDATUS.
PLATE XI.

Mus longicaudatus, _Bennett_, Proceedings of the Committee of Science
and Correspondence of the Zoological Society of London for January,
1832, p. 2.

_M. pallidè flavescenti-fuscus; corpore subtùs albo, levitèr flavo
lavato; pedibus albis; tarsis permagnis; caudâ perlongâ; auribus
parvulis._

DESCRIPTION.—Fur long and soft; general colour pale yellow-brown, the
hairs of the ordinary fur being fulvous near the apex, and the
longer hairs brown. On the sides of the body, cheeks, and external
side of limbs, the fulvous hue prevails. The inner side of the
limbs and the under parts of the body are white, but have an
indistinct yellowish hue. All the hairs of the body are of a deep
gray colour at the base. The ears are small, well clothed with
hairs; those on the inner side are chiefly yellow; externally, on
the fore part they are brown, and posteriorly whitish. The feet
are of a flesh-colour, and furnished above with white hairs; the
tarsi are but sparingly provided with minute hairs on the upper
side, and are naked beneath: they are of unusually large size. The
fore feet are of moderate[18] size, and furnished with a very
large carpal tubercle. The tail is very nearly double the length
of the body, if the latter be measured in a straight line; it is
of a brownish flesh-colour above, paler beneath, and sparingly
furnished with minute bristly hairs; those on the upper surface
being brown, and on the under side white. The hairs of the
moustaches are long, of a black colour, and grayish at the apex.

In. Lines.
Length from nose to root of tail 3 9
of tail 5 3
from nose to ear 0 10½
of tarsus (claws included) 1 1
of ear 0 4

Habitat, Chile.

The most conspicuous characters of the present species consist in the immense length of the tail, and the great size of the hinder feet.[19] It is about equal in size to _Mus Musculus_; its form, however, is somewhat stouter; in colour it is much paler and brighter. The head is larger in proportion; the ears are smaller, and more densely clothed with hair; the fore feet are rather larger, and the fleshy tubercle on the under side of the wrist is also larger. The thumb nail is flattened, and rounded at the tip, as in _Mus Musculus_, but is longer, and more distinct than in that animal.

The skull of _M. longicaudatus_, (Plate 34, Fig. 1,) is considerably larger than that of the common mouse, but in form scarcely differs from it; its upper surface is rather more convex, and the interparietal bone proportionately less. The length of the skull is 1 inch; breadth, 6½ lines; distance between the forepart of the incisor, and the first molar of the upper jaw, 3½ lines. The dentition is figured in Plate 34, Figs. 1. _b_ and 1. _c_.

The above account is drawn up from the same specimen as that from which Mr. Bennett took his description, and which was brought from Chile by Mr. Cuming, who states that the animal in question lives in trees, and constructs its nest with grass.

In Mr. Darwin’s collection, I find an animal which agrees in all the more important characters with the one above described, but differs in being of a deeper colour, (approaching more nearly, in this respect, to the common mouse,) and in having the tail a trifle shorter. The skull is about ¾ of a line shorter, but its proportions agree precisely: the proportions of the feet, and the general form of the animal, also agree. This specimen is likewise from Chile, (Lat 37° 40′,) and, according to Mr. Darwin, “overran the wooded country south of Concepcion, in swarms of infinite numbers. Captain FitzRoy, on his return from visiting the wreck of H. M. S. Challenger, had the kindness to bring me this specimen. So destructive was this little animal, that it even gnawed through the paper of the cartridges belonging to the people who were wrecked.”—D.

MUS ELEGANS.
PLATE XII.

Mus elegans, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 19.

Eligmodontia typus, _F. Cuvier_, Annales des Sciences Naturelles for
March 1837. Tom. 7. p. 169. Pl. 5.

_M. suprà flavus, vellere pilis fuscescentibus adsperso, his ad
latera, et prope oculos rarioribus; pilis pone aurem utramque,
labiis, corpore subtùs, pedibusque niveis; auribus magnis; caudâ
capite corporeque paulo longiore; tarsis longis subtùs pilis
obsitis._

DESCRIPTION.—Fur very long and soft; general colour of the upper parts
of the body pale brownish yellow; the lower portion of the cheeks,
and the under parts of the body pure white: the hairs of the
ordinary fur of the back are gray at the base, pale ochre near the
apex, and brown at the apex; the longer hairs are brownish. On the
sides of the body where the longer hairs are less numerous, the
pale ochre colour prevails; the hairs on this part as on the back
are deep gray at the base, but at a short distance from the apex
they are white; nearer the tip shaded into yellow, and at the tip
brownish: the limbs externally are of a pale yellow colour. The
hairs of the throat and chest are pure white to the root, those on
the belly are obscurely tinted with gray at the root. The feet are
of a pale flesh-colour, and furnished with white hairs; the fore
feet are of moderate size; the thumb nail is small and rounded,
and the carpal tubercle is covered with hairs; the tarsi are long,
and the white hairs extend over the whole of the under parts; the
under side of the toes, however, are but sparingly furnished.
There appears to be but one large tubercle on the under side of
the tarsus, and this, which is situated near the base of the toes,
is thickly covered with silvery-white hairs. The tail is long,
pale brown above, and pale flesh-colour beneath; above, it is
furnished with minute brown hairs, and on the under side with
white hairs. The ears are rather large, of a pale flesh-colour,
tolerably well clothed with hairs, which are of a pale yellow
colour on the inner side, and white on the outer side—excepting on
the fore part, where they are brown. A small tuft of white hairs
springs from the base of the ear posteriorly. The hairs of the
moustaches are moderate; black at the base, and grayish at the
apex.

In. Lines.
Length from nose to root of tail 3 7
of tail 3 9
from nose to ear 1 0
of tarsus 0 10
of ear 0 6

Habitat, Bahia Blanca, (_September_.)

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

Habitat, Maldonado, La Plata, (_June_.)

The skull of this animal, is rather shorter and broader than that of _Mus Musculus_, the upper surface is more arched, the zygomatic arch is much more slender, and the nasal bones are rather broader. In the convexity of the upper surface, and the slenderness of the zygomatic arch, this skull very nearly resembles that of _M. gracilipes_; this latter, however, has the zygomatic arch more convex, projecting more suddenly on the anterior part, and the interparietal bone smaller. Length of skull 10 lines, width 5½, length of nasal bones 4 lines, distance between the outer side of the incisors, of the upper jaw, and the first molar 2⅞ lines. See Plate 34, fig. 3. _a_.

The dentition is figured in Plate 34, figs. 3. _b_ and _c_.

This mouse is rather less than _M. Musculus_, the tail is much shorter in proportion, the fur is longer and softer, and the ears are more distinctly clothed with hair.

The pale and delicate yellow colour of the upper parts of the body, and the pure white of the under parts, renders the present species conspicuous amongst its congeners. I may further remark that the white colour which in the Muridæ (when it occurs) is usually confined to the under part of the body, or extends but slightly on the sides, is in the present animal extended considerably on the sides of the body, and occupies an equal portion with the yellow of the upper parts. The name _bimaculatus_ is applied to this animal on account of the two conspicuous white patches, which are situated behind the ears.

In affinity as well as in appearance it most nearly approaches to _Mus gracilipes_ and _M. elegans_; with no other species of the genus _Mus_, here described, can it be confounded, since these only have the tarsus hairy beneath.

The principal points of distinction between the present animal and _Mus elegans_, are noticed in the account of that species.

“This mouse, when alive, had a very elegant appearance. A countryman, who brought it me, found six of them living together in one burrow.”—D.

MUS GRACILIPES.
PLATE XI.

Mus gracilipes, _Waterh._, Proceedings of the Zoological Society of
London, for February 1837, p. 19.

_M. suprà flavo-lavatus; pilis pone aurem utramque, labiis, corporeque
subtùs, albis; pedibus parvulis, gracilibus, carneis, suprà et ad
calcem pilis albis tectis; caudâ gracili, pilis albis instructâ,
quoad longitudinem corpus ferè æquante; auribus mediocribus; vellere
mediocri et molli, pilis omnibus ad basin plumbeis._

DESCRIPTION.—General colour very pale yellowish brown, a tint produced
by the admixture of black and pale fawn colour; the hairs of the
ordinary fur being of the latter tint near the apex, and dusky at
the apex, whilst the longer hairs are black. The feet, tail, under
parts of the body and the sides of the muzzle, are pure white. All
the hairs of the body, (which are soft, and of moderate length),
are deep gray at the base. The ears are of moderate size, well
clothed with hairs, of which those on the inner side are
yellowish, and those on the outer, are brown on the anterior part,
and white on the posterior. A small tuft of white hairs springs
from the neck immediately behind the ears; this tuft is hidden
when the ears are folded back. The tail is slender and short,
(being not quite equal to the body in length) of a pale
flesh-colour, and sparingly furnished with minute white hairs. The
feet are very small and slender, and the naked parts are of a pale
flesh-colour. The sole of the foot is covered with hairs; the toes
beneath, and the tubercles (which are as in _Mus Musculus_),
however, are naked. The hairs of the moustaches are of moderate
length, and of a blackish colour, some of them, however, are
grayish white.

In. Lines.
Length from nose to root of tail 2 10
of tail 1 7
from nose to eye 0 4⅓
from nose to ear 0 8¼
of tarsus (claws included) 0 6½
of ear 0 4¼

Habitat, Bahia Blanca, (_September_.)

This species slightly exceeds the harvest mouse (_Mus messorius_) in size, its ears are considerably larger in proportion, and the tail is shorter. Compared with the common mouse (_Mus Musculus_) it is smaller, the tail is more slender, and shorter, and the feet are likewise more slender and proportionately much smaller; the ears are more distinctly clothed with hairs.

The principal points of distinction between this and the two preceding species are pointed out in the account of _M. elegans_.

Upon comparing the skull of _M. gracilipes_ (Pl. 34, fig. 4. _a_.) with that of _Mus Musculus_, the most striking differences consist in its shorter and broader form, the upper surface being more arched, the interparietal bone has a relatively smaller antero-posterior diameter, the occipital region is more convex, and continued more gently and gradually into the upper region of the skull. The zygomatic arch, which is unusually slender, is more dilated (especially on the anterior part) thus giving a squareness to the general form. The nasal bones are not so much attenuated posteriorly. The length of the skull is 8⅞ lines, the greatest width is 5⅛ lines, and the distance between the outer side of the incisors and the front molar is 2¾ lines.

The dentition is figured in Plate 34, figs. 4. _b_ and 4. _c_.

“This specimen was given me by Mr. Bynoe, the surgeon of the Beagle, who caught it amongst some long dry grass.”—D.

MUS FLAVESCENS.
PLATE XIII.

Mus flavescens, _Waterh._, Proceedings of the Zoological Society of
London, for February 1837, p. 19.

_M. suprà colore cinnamomeo, lateribus capitis, corporisque, æquè ac
pectore, auratis; gulâ abdomineque flavescenti-albis: pedibus
sordidè albis: auribus mediocribus rotundatis, pilis flavis obsitis:
caudâ, corpore, capiteque longiore, suprà fuscâ, subtùs sordidè
albá: tarsis longis._

DESCRIPTION.—Fur long and moderately soft; general colour of the upper
parts bright brownish yellow; on the sides of the head and body
bright yellow; towards the rump of a deeper hue, and inclining to
orange; under parts pale yellow, or yellow-white; chest yellow.
The fur both of the upper and under parts of the body deep
plumbeous at the base. Feet flesh-colour, covered above with white
hairs: tarsi long, naked beneath. Ears small, tolerably well
clothed with hairs; those on the inner side yellow, but many of
them blackish at the base; on the outer side, the hairs are
blackish on the fore part and yellow on the hinder part. The hairs
of the ordinary fur of the back are of a deep rich yellow colour
at the tip, and the longer hairs are blackish. The tail is long,
deep brown above and whitish beneath, the hairs of the moustaches
are rather short and slender, and of a brownish colour. Thumb nail
small and rounded.

In. Lines.
Length from nose to root of tail 3 9
of tail 4 1½
from nose to ear 1 0
of tarsus 1 0½
of ear 0 4½

Habitat, Maldonado, La Plata, (_June_.)

This species is slightly larger than the common mouse; the head is rather larger in proportion; the ears are rather smaller and more distinctly clothed with hair; the tail and tarsi are much longer in proportion. Its bright yellow colouring and proportions distinguish it from any of the species described in this work. Of this animal I do not possess the skull, nor of the teeth do I possess more than the first and second molars of the upper jaw, and the second and last of the lower jaw. These are figured in Plate 34, figs. 5. _a_, and 5. _b_.

MUS MAGELLANICUS.
PLATE XIV.

Mus Magellanicus, _Bennett_, Proceedings of the Zoological Society of
London for December 1835, p. 191.

_M. suprà fuscus, subtùs cinerescenti-albus, pallidè flavo lavatus;
auribus mediocribus pilis fuscis obsitis; caudâ corpus caputque
æquante; tarsis longis, pilis sordidè albis obsitis._

DESCRIPTION.—Fur very long and moderately soft, general colour deep
brown; the hairs of the ordinary fur are gray, tipped with
yellowish brown; the longer hairs are black; the sides of the body
are yellowish; the under parts are gray-white with a faint
yellowish tint, each hair being gray tipped with yellowish white.
The ears are rather small, well clothed with hairs; those on the
inner side are blackish tipped with yellow, and on the outer side
they are blackish on the fore part and dusky on the hinder part.
The fore feet are of moderate size, the thumb nail is short and
rounded; the tarsi are rather long; both fore and hinder feet are
of a brownish colour, and covered above with dirty gray hairs. The
tail rather exceeds the head and body in length; it is brown above
and dirty white beneath. The hairs of the moustaches are numerous
and long, of a brownish colour at the apex and black at the base.

In. Lines.
Length from nose to root of tail 4 3
of tail 4 2
from nose to ear 1 0½
of tarsus 1 1
of ear 0 5

Habitat, Port Famine, Strait of Magellan.

This mouse is larger than _Mus Musculus_; the tail is rather longer in proportion; the tarsi much longer; the ears are not quite so large in proportion to the head, (which greatly exceeds that of _Mus Musculus_ in size,) and they are densely clothed with hair. The fur is longer. In colour, the animal here described is rather darker than the common mouse. I have one specimen however before me which _very nearly_ agrees in this respect.

The dentition is figured in Plate 34, figs. 6, _a._ and 6, _b_.

From the attention which Mr. Darwin bestowed upon the Muridæ of the southern parts of South America, I presume his collection affords materials for a tolerably complete monograph of the species of that portion of the globe. The species above described, however, does not occur in Mr. Darwin s collection, but is here introduced in order to make the work more complete, and that I might more clearly point out the distinctions which exist between it and other species here described, the account given by Mr. Bennett in the Proceedings being very short.

MUS ARENICOLA.
PLATE XIII.

Mus arenicola, _Waterh._, Proceedings of the Zoological Society of
London, for February 1837, p. 18.

_M. suprà fuscus, subtùs cinerescenti-albus, pallidè flavo tinctus;
auribus mediocribus rotundatis, pilis flavis fuscisque obsitis;
caudâ quoad longitudinem corpus æquante; pedibus cinerescenti-albis:
tarsis mediocribus._

DESCRIPTION.—Fur long, moderately soft; general colour deep brown;
sides of the body with a very obscure yellowish hue; under parts
dirty gray with a faint yellow tint. All the fur deep gray at the
base; the hairs of the upper part of the body obscurely annulated
with yellowish brown near the apex, and dusky at the apex; the
longer hairs are black. Feet brownish, covered above with
brown-white hairs; tarsi short. Tail short, blackish above,
brown-white beneath. Ears small, well clothed with hairs; those on
the inner side are yellow at the apex and gray at the base; on the
outer side they are of a brownish colour, and on the fore part
blackish. The hairs of the moustaches are short and slender, and
of a brownish colour. The head is large.

In. Lines.
Length from nose to root of tail 4 3
of tail 2 9
from nose to ear 1 0
of tarsus (claws included) 0 10
of ear 0 4½

Habitat, Maldonado, La Plata, (_June_.)

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

Habitat, Chonos Archipelago, (_December_.)

This mouse is considerably larger than _Mus Musculus_, and the great length and density of its fur, causes it to appear much stouter in its proportions; its colouring is darker, the tips of the hairs being much more narrowly annulated with yellow than in that species. The very small size of the ears will serve to distinguish the present animal from its congeners—_Mus longipilis_, _M. Renggeri_, _M. arenicola_, &c.

The molar teeth of the upper jaw are figured in Plate 34. fig. 8, _a_; and fig. 8, _b_, represents the middle and last molars of the lower jaw.

“Inhabited a very small island, covered with thick forest, in the central part of the Chonos Archipelago.”—D.

A mouse obtained on the islets adjoining the east coast of Chiloe (where Mr. Darwin says it was common) differs from the above in being a little smaller, the tail is rather longer, and the ears are a trifle larger. In the feet, claws, colouring and character of the fur it agrees, and likewise in the pale colour and slenderness of the incisors. Its dimensions are as follows:—

In. Lines.
Length from nose to root of tail 4 0
of tail 3 0
of tarsus (claws included) 0 10
from nose to ear 0 10½
of ear 0 4

I have not the means of satisfying myself whether this be a distinct species or not; but I think it is not.

“The nature of the country where this specimen was procured is nearly the same as in that part of the Chonos Archipelago, 150 miles to the south, where the first was obtained.” D.

14. MUS RENGGERI.
PLATE XV.—Fig. 1.

Mus olivaceus, _Waterh._, Proceedings of the Zoological Society of London, for February 1838, p. 16.

_M. corpore suprà subolivaceo, subtùs cinerescente; auribus
mediocribus, rotundatis, pills parvulis fuscescentibus obsitis;
caudâ corpore breviore, pilosâ, suprà fuscâ subtùs albescente;
pedibus pilis fuscescentibus tectis._

DESCRIPTION.—Fur moderate; ears moderate; tail shorter than the body;
general colour gray washed with yellow; under parts grayish white.
On the upper parts and sides of the head and body the hairs are
gray, broadly annulated with yellow near the apex, and dusky at
the apex; the mixture producing a yellowish gray tint, approaching
somewhat towards olive:—the hairs on the under parts of the body
and throat are deep gray at the base, and white at the apex; the
hairs of the feet are brownish-white. The tail is tolerably well
clothed with hairs; those on the upper surface are brown, and
those on the under are dirty white. The ears are well clothed,
both externally and internally, with hairs of the same colour as
those on the upper parts of the body. The hairs of the moustaches
are for the most part whitish, and black at the base. The upper
incisors are pale yellow, and the lower incisors are yellowish
white.

In. Lines.
Length from nose to the root of tail 5 1
of tail 2 8
from nose to base of ears 1 2
of tarsus (claws included) 0 11
of ear. 0 5

Habitat, Valparaiso (_August and September_,) Coquimbo (_May_.)

Subsequent to the description of this species, under the name of _M. olivaceus_ in the Zoological Society’s Proceedings, I have imagined that perhaps that name might mislead as regards the colouring of the animal;—it certainly has a slight olive hue, but it is not very evident. I have therefore changed the name, and substituted that of the author of the “Naturgeschichte der Säugethiere von Paraguay,” &c.

In the collection there are three specimens of the present species; in one of these the hairs of the upper part and sides of the body are annulated with yellowish white, instead of yellow; hence the general hue of these parts is nearly gray.

_Mus Renggeri_ is larger than _Mus Musculus_, and much stouter in its proportions; the fur is shorter, much less dense, and less soft than in _Mus brachiotis_.

“It inhabits dry stony places, where only a few thickets grow.”—D.

15. MUS OBSCURUS.
PLATE XV.—Fig. 2.

Mus obscurus, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 16.

_M. suprà fusco-nigrescens, subtùs flavescens; pedibus obscurè fuscis;
unguibus longiusculis; auribus mediocribus; caudâ corpore breviore,
suprà nigrescente, subtùs sordidè albâ; vellere mediocri, molli._

DESCRIPTION.—Head large; ears moderate; tail shorter than the body;
fur rather long and glossy; the general hue of that of the upper
parts and sides of the head and body is blackish brown, and that
of the under parts is dirty yellowish white. The hairs on the
upper parts are of a deep lead colour at the base, black at the
apex, and narrowly annulated with dark yellow near the apex; those
of the throat and belly are lead colour at the base and yellowish
at the tip; the chin is white: around the eye, and on the lower
part of the cheeks a deep yellow tint prevails. The ears are well
clothed with hairs both externally and internally, and these are
for the most part of a deep brown colour, as are also the hairs
which cover the feet. The tail is well clothed with hairs, those
on the upper surface are black, and those on the under are dirty
white. Both upper and lower incisors are yellow, but the lower are
paler than the upper.

In. Lines.
Length from nose to root of tail 5 3
of tail 2 7
from nose to ears 1 2½
of tarsus (claws included) 0 11½
of ear 0 4

Habitat, Maldonado, La Plata, (_June_.)

The present species, like the foregoing, is much stouter than the common mouse (_Mus Musculus_), its colour is much darker. In possessing a glossy fur it differs from most of its congeners; its head is also proportionately larger, and the incisors are much stronger.

The molars of the upper jaw are figured in plate 34, fig. 9, _a_,—and fig. 9, _b_, represents those of the under jaw.

“Very abundant in gardens and hedges, far from houses; and was easily caught in traps baited either with cheese or meat.”—D.

16. MUS XANTHORHINUS.
PLATE XVII.—Fig. 1.

Mus xanthorhinus, _Waterh._, Proceedings of the Zoological Society of
London, for January 1837, p. 17.

_M. suprà fuscus flavo lavatus; subtùs albus; rhinario flavo; auribus
parvulis, intùs pilis flavis obsitis; mystacibus longis, canis, ad
basin nigrescentibus: caudâ corpore breviore, suprà fuscâ, ad latera
flavescente, subtùs sordidè albâ: pedibus anticis, tarsisque flavis,
digitis albis: vellere longo, molli._

DESCRIPTION.—Fur moderately long and loose; ears rather small; tail
shorter than the body; general colour gray washed with yellow, the
yellow colour prevailing, especially on the sides of the body;
muzzle, inner side of ears, and tarsus, of a rich yellow colour;
toes, chin, throat, under parts of body, and rump, white; all the
fur deep gray at the base; the hairs on the upper parts and sides
of the body broadly annulated near the apex with rich yellow, and
at the apex dusky; on the under parts of the body the hairs are
broadly tipped with white. Tail rather sparingly furnished with
hair, that on the upper surface brown, on the sides yellow, and on
the under surface whitish. The hairs of the moustaches are
white—some of them dusky at the base. The incisor teeth are rather
slender, and of a pale yellow colour.

In. Lines.
Length from nose to root of tail 3 6
of tail 1 7½
from nose to ear 0 10
of tarsus (claws included) 0 9
of ear 0 3¾

Habitat, Hardy Peninsula, Tierra del Fuego, (_February_.)

The white, which is usually confined to the under parts of the body, in this species extends slightly on the sides of the body, and the lower portion of the cheeks.

“This species was caught on the mountains, thickly covered with peat, of Hardy Peninsula, which forms the extreme southern point of Tierra del Fuego.”—D.

17. MUS CANESCENS.

Mus canescens, _Waterh._, Proceedings of the Zoological Society of
London for February, 1837, p. 17.

_M. suprà canescens, subtùs albus; oculis flavido cinctis; auribus
parvulis, pilis pallidè flavis et plumbeis obsitis; mystacibus
mediocribus, canis, ad basin nigricantibus; caudâ vix corpore
breviore, suprà fusco-nigrâ, subtùs sordidè albâ; pedibus anticis
tarsisque flavescentibus._

DESCRIPTION.—Fur moderately long and loose; ears small; tail nearly
equal to the body in length: general colour gray, with a wash of
very pale yellow; chin, throat, and under parts of the body,
white. Tail tolerably well clothed with hairs, those on the upper
surface brown, and those on the under, whitish; on the sides are
some yellowish hairs. Ears with yellow hairs on the inner side;
tarsi pale yellow, toes white; muzzle and around the eye
yellowish.

In. Lines.
Length from nose to root of tail 3 6[21]
of tail 2 1
from nose to ear 1 1
of tarsus (claws included) 0 9½
of ear 0 4

Habitat, Santa Cruz and Port Desire, (_December_.)

“Very common in long dry grass in the valleys of Port Desire.”—D.

The skull is figured in Plate 33, fig. 5, _c_. Fig. 5, _a._ represents the molars of the upper jaw; fig. 5, _b._ those of the under jaw, and fig. 5, _d._ represents the posterior molar of the under jaw when more worn.

It was with some hesitation that I described this as a distinct species in the Society’s Proceedings. I have now re-examined the specimens, and still am unable to satisfy myself whether they are varieties of _Mus xanthorhinus_ or not. Both of _Mus canescens_ and of _Mus xanthorhinus_, I have before me what I imagine to be an adult and a young specimen. The adult and the young of _M. xanthorhinus_ agree in being of a _yellowish brown_ colour, and in having the muzzle and tarsi deep yellow; both specimens of _Mus canescens_ are of a _gray_ colour, with an indistinct yellow wash, the muzzle and tarsi being tinted with yellow, as in _M. xanthorhinus_. Besides this difference in tint, which, perhaps, is unimportant, _M. canescens_ differs from _M. xanthorhinus_ in having the head larger, the tail rather longer, and the fur less soft. The specimens of this animal are both from Patagonia; one of the specimens of _Mus xanthorhinus_ was brought by Mr. Darwin from Terra del Fuego; and as the other formed part of Captain King’s collection, it in all probability came from the same locality. As I only possess one skull, I cannot speak with certainty as regards the size of the head; the difference, however, in the stuffed specimens is considerable, and it is strange that each of the pairs should agree so perfectly, supposing the difference to be the work of the stuffer’s hands.

18. MUS LONGIPILIS.
PLATE XVI.

Mus longipilis, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 16.

_M. suprà obscurè griseus, flavo lavatus; subtùs griseus; pedibus
fuscis, unguibus longiusculis; auribus mediocribus; caudâ corpore
breviore, suprà nigrescente, subtùs fuscescente; rhinario
sub-producto: vellere longissimo, molli._

DESCRIPTION.—Fur very soft and silky, and extremely long—the ordinary
fur of the back measuring nearly three quarters of an inch, and
the longer hairs one inch in length; ears moderate; tail nearly as
long as the body; muzzle much pointed; general colour gray, washed
with yellow, the under parts pale gray, or grayish white; feet
brown; ears and tail well clothed; the hairs on the inner side of
the ears are chiefly of a yellow colour, those on the upper
surface of the tail are brown-black, those on the under part are
dirty white; the hairs of the back are deep gray at the base,
broadly annulated with yellow near the apex, and dusky at the
apex; the longer hairs are grayish black; the hairs of the
moustaches are dusky at the base, and whitish beyond that part;
the claws are long, and but slightly curved; the incisors are
slender; those on the upper jaw are yellow, and those of the under
yellow-white.

In. Lines.
Length from nose to root of tail 5 4
of tail 3 4
from nose to ear 1 2
of tarsus (claws included) 1 0½
of ear 0 6½

Habitat, Coquimbo, Chile, (_May_.)

This mouse is remarkable for the great length and softness of its fur, even among the species here described, most of which have very loose, long and soft fur.

The molars of the upper jaw are figured in Plate 33, fig. 6, _b._—molars of the lower jaw, fig. 6, _a_.

“Inhabits dry stony places, which character of country is general in this part of Chile.”—D.

19. MUS NASUTUS.
PLATE XVII.—Fig. 2.

Mus nasutus, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 16.

_M. suprà obscurè flavescenti-fuscus, ad latera fulvescens; subtùs
obscurè fulvo tinctus: pedibus pilis obscurè fuscis tectis; unguibus
longis; auribus mediocribus; caudâ corpore breviore, suprà fuscá,
subtùs sordidè albâ: rhinario producto._

DESCRIPTION.—Muzzle very long and pointed, ears small, tail shorter
than the body, claws long and but slightly arched; inner,
rudimentary toe of the fore foot furnished with a pointed claw;
fur moderate, and slightly glossy: general colour yellowish brown,
of the sides of the body yellow, of the under parts pale yellow;
the chin, throat and chest whitish: feet brown; ears well clothed
with hairs, those on the inner side are most of them yellow, but
some are black. All the fur is of a deep lead colour at the base;
the hairs on the upper parts and sides of the head and body are
broadly annulated with deep golden yellow near the apex, and
blackish at the apex; on the upper parts long brownish black hairs
are thickly interspersed with the ordinary fur, but on the side of
the body they are less numerous, hence on this part the yellow
tint prevails; on the under parts of the body the hairs are
broadly tipped with pale yellow, and in parts with white: the tail
is but sparingly clothed with hairs, those on the upper surface
are of a dark brown colour, and those on the under are pale brown.
The incisors are very slender and of a very pale yellow colour.

In. Lines.
Length from nose to root of tail 5 2
of tail 2 8
from nose to ear 1 3
of tarsus (claws included) 1 0½
of ear 0 5

Habitat, Maldonado, La Plata, (_June_.)

The specific name _nasutus_ has been applied to this mouse on account of its elongated and slender muzzle[22], the tip of which extends nearly 4 lines beyond the upper pair of incisors: the rudimentary toe of the fore foot, instead of having the usual rounded nail, has a short pointed claw. Its fur is not so soft, nor yet so long as in many of the preceding species, and there is a greater admixture of yellow in its colouring. The claws appear to be adapted to burrowing.

The skull (which is not quite perfect) is figured in Plate 33, fig. 7, _a_, its length is 1 in. 3 lines. Fig. 7, _b_, represents the molars of the upper jaw, and fig. 7, _c_, those of the under jaw. The lower jaw, which is of a very slender and elongated form, is figured in Plate 34, fig. 10, _a_.

“Was caught in a small thicket on an open grassy plain, by a trap baited with a piece of bird. This mouse when alive possesses a marked character in the extreme acumination of its nose.”—D.

20. MUS TUMIDUS.
PLATE XVIII.

Mus tumidus, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 15.

_M. brunneus, nigro lavatus; rostro ad apicem, labiis, mento, gulâ,
pectore, abdomineque albis; naso suprà nigrescente; auribus
mediocribus rotundatis; corpore crasso; caudâ capite corporeque
breviore, pilis nigricantibus, subtùs albescentibus prope basin,
vestitâ; artubus pedibusque grisescentibus; vellere longo, molli;
unguibus longis._

DESCRIPTION.—Body stout; head large; tail nearly as long as the head
and body; inner toe of the fore foot with a distinct, pointed
claw; claws rather large, those of the fore feet but slightly
arched. Fur rather long, and moderately soft; general tint of the
upper parts of the body, brown, of the sides of the head and body,
grayish, but with a yellow wash; the lower part of the sides of
the body and of the cheeks, the tip of the muzzle, and the whole
of the under parts, white; feet dirty white; ears densely clothed
with short hairs, those on the inner side chiefly of an ashy-brown
colour, and those on the outer side dusky; the hairs of the back
are of a deep lead colour at the base, black at the tip, and
annulated with yellow near the tip; the longer hairs, which are
thickly interspersed, are totally black; on the under parts of the
body the hairs are gray at the base, and broadly tipped with
white; the upper surface of the muzzle is blackish; the moustaches
are black; the incisors are yellow.

In. Lines.
Length from nose to the root of tail 6 9
of tail 5 4
from nose to ears 1 8
of tarsus (claws included) 1 6
of ear 0 7

Habitat, Maldonado, La Plata (_June_.)

This species is about the size of _Mus Rattus_, but is stouter in its proportions; as in _Mus nasutus_, the thumb is furnished with a pointed claw. The molars of the lower jaw are figured in Plate 34, fig. 11, _a_.

“This rat was caught in so wet a place amongst the flags bordering a lake, that it must certainly be partly aquatic in its habits.”—D.

21. MUS BRAZILIENSIS.
PLATE XIX.

Rat du Brézil, _Geoff._

_M. suprà fuscus fulvo lavatus; lateribus capitis corporisque æquè ac
abdomine auratis; gulâ pectoreque albis; pedibus pilis sordidè
flavis tectis; auribus parvulis; caudâ caput corpusque ferè æquante;
vellere longo, molli._

DESCRIPTION.—Head somewhat arched, and rather short; ears small; tail
about equal in length to the head and body, measured in a straight
line; tarsi large. Fur long, and rather soft; general colour deep
golden yellow: on the upper surface of the head and the back, long
glossy black hairs are thickly interspersed, and produce, with the
admixture of the deep golden colour of the ordinary fur, a dark
brown tint; chin, throat, chest, and rump, white; the hairs
covering the upper surface of the feet are of a dirty yellowish
white colour, and on the toes nearly white: ears densely clothed
with longish hairs, those on the inner side chiefly of a deep
golden colour, and those on the outer side brownish; the ears are
partially hidden by the long fur of the head; tail sparingly
clothed with hairs, above brown, and beneath brownish-white: the
fur of the back is of a deep gray colour at the base, annulated
with deep golden yellow near the apex, and blackish at the apex;
the longer hairs are black; the hairs of the belly are pale gray
at the base, and broadly tipped with golden yellow colour; the
white hairs on the throat, chest, and rump are of an uniform
colour—not tinted with gray at the root;—the hairs of the
moustaches are black: the incisors of the upper jaw are of a deep
orange colour, and those of the lower jaw are yellow: the thumb
nail is truncated.

In. Lines.
Length from nose to root of tail 8 6
of tail 7 9
from nose to ear 1 8
of tarsus 2 0
of ear 0 6½

Habitat, Bahia Blanca, (_September_.)

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.