Chapter IV: Part 4

“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

Habitat, Santa Cruz, Patagonia, (_April_.)

The molars of the upper jaw are figured in Plate 34, fig. 13, _a_, and those of the lower jaw, fig. 13, _b_.

“Caught in the interior plains of Patagonia in lat. 50°, near the banks of the Santa Cruz.”—D.

23. MUS GRISEO-FLAVUS.
PLATE XXI.

Mus griseo-flavus, _Waterh._, Proceedings of the Zoological Society of
London for February 1837, p. 28.

_M. suprà griseus flavo-lavatus, ad latera flavus, subtùs albus;
pedibus albis; auribus magnis et ferè nudis; caudâ caput corpusque
ferè æquante, suprà fusco-nigricante, subtùs albâ; vellere longo,
molli._

DESCRIPTION.—Ears large; tail rather shorter than the head and body
taken together; tarsi slender, and moderately long; fur long and
very soft; general tint of the upper parts of head and body
grayish, washed with brownish yellow; on the sides of the body a
palish yellow tint prevails; feet, chin, throat, and under parts
of body pure white; tail rather sparingly clothed with hairs,
those on the apical portion rather long, and forming a slight
pencil at the tip; on the upper side and at the tip of the tail
the hairs are brown, on the under side they are dirty white; the
ears are very sparingly clothed with minute brownish yellow hairs
internally; externally, on the fore part, the hairs are rather
longer and of a brown colour; the upper incisors are orange, and
the lower incisors are yellow; the hairs of the moustaches are
long, and of a black colour; the hairs of the back are deep gray
at the base, brownish at the tip, and annulated with pale brownish
yellow near the tip; the longer hairs are brown; the hairs of the
belly are white externally, and gray at the base; on the throat
the hairs are white to the root.

In. Lines.
Length from nose to root of tail 6 8
of tail 5 6
from nose to ear 1 4½
of tarsus (claws included) 1 2½
of ear 0 8

Habitat, Northern Patagonia (_August_.)

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]

Habitat, Coquimbo, Chile, (_May_.)

This species is evidently allied to the two preceding; and perhaps the “Rat quatrieme, ou Rat oreillard” of Azara, (_Mus auritas_, Desm.) will form one of this little group. The molar teeth of the upper jaw are figured in Plate 34, fig. 17, _a_—those of the lower jaw, fig. 17, _b_.

“Inhabits dry stony places.”—D.

26. MUS GALAPAGOENSIS.
PLATE XXIV.

_M. suprà fuscus, flavo-lavatus, ad latera flavescens, subtùs albus:
pedibus pilis sordidè albis tectis: auribus mediocribus; caudâ,
quoad longitudinem, caput corpusque ferè æquante: vellere longo._

DESCRIPTION.—Ears moderate, slightly pointed; tarsi moderate; tail
slender, nearly as long as the head and body; fur long, and not
very soft; upper parts of the body of a brownish hue, a tint
produced by the admixture of black and palish yellow hairs; on the
sides of the body the longer black hairs are less abundant, and
the prevailing colour is yellow; under parts of the body white,
with a very faint yellow tint; feet furnished above with dirty
white hairs; ears rather sparingly clothed with hairs, those on
the inner side of a yellow colour, and those on the outer side
dusky; tail above brown, and beneath whitish; the hairs of the
moustaches black; the incisors deep yellow; the hairs on the back
are deep gray at the base, broadly annulated with palish yellow
near the apex, and blackish at the apex; the longer hairs black;
on the belly the hairs are gray at the base, and broadly tipped
with yellowish white.

In. Lines.
Length from nose to root of tail 6 0
of tail 4 9
from nose to ear 1 3¾
of tarsus (claws included) 1 2
of ear 0 7

Habitat, Chatham Island, Galapagos Archipelago, Pacific Ocean,
(_October_.)

This species is less than _Mus Rattus_. The upper parts of the body have a slightly variegated appearance.

The skull of _Mus Galapagoensis_ (Plate 33, fig. 8, _a_,) is rather smaller than that of _M. Rattus_, the nasal portion is proportionately longer, the cranial shorter, and the interparietal bone is smaller, especially in antero-posterior extent; its length is 15 lines, and its breadth is 8⅛ lines. The lower jaw is figured in Plate 34, fig. 14, _a_. Fig. 8, _b_, of Plate 33, represents the molars of the upper jaw, and fig. 8, _c_, those of the lower jaw.

“This mouse or rat is abundant in Chatham Island, one of the Galapagos Archipelago. I could not find it on any other island of the group. It frequents the bushes, which sparingly cover the rugged streams of basaltic lava, near the coast, where there is no fresh water, and where the land is extremely sterile.”—D.

27. MUS FUSCIPES.
PLATE XXV.

_M. suprà fusco-nigrescens, subtùs griseus; pedibus fuscis; auribus
mediocribus, caudâ, quoad longitudinem, caput corpusque ferè
æquante: vellere longissimo, molli._

DESCRIPTION.—Form stout; ears moderate; tail equal to the body in
length; tarsi moderate; fur very long. General tint of the upper
part and sides of the head and body blackish brown with an
admixture of gray; of the under parts grayish white; feet brown,
the hairs grayish at the tip: tail black and but sparingly clothed
with short bristly hairs: ears rather sparingly clothed with
hairs, which are for the most part of a brownish gray colour. The
ordinary fur of the back is about ¾ of an inch in length and very
soft—of a deep gray colour, broadly annulated with brownish yellow
near the tip and blackish at the tip: the longer hairs which are
black, measure upwards of 1¼ inches in length. The upper incisors
are of an orange colour and the lower are black.

In. Lines.
Length from nose to root of tail 6 6
of tail 4 3
from nose to ear 1 6
of ear 0 6½
of tarsus (claws included) 1 1

Habitat, Australia, King George’s Sound, (_March_.)

Mammalia not belonging to the order _Marsupiata_ are rare in the Continent of Australia. Besides the Dog, we are acquainted with none excepting a few species of Rodents, and these all belong to the family _Muridæ_.

The present animal adds one to the limited number already known: in the Museum of the Zoological Society there is another species, the characters of which I will point out in the next description.

_Mus fuscipes_ is remarkable for the great length and softness of its fur, and the brown colour of its feet: it is rather less than _Mus Rattus_, and of a stouter form. Not having had an opportunity of examining the molar teeth and the cranium of this animal, I cannot be positive that it is a species of the genus _Mus_; in external characters and the form of the incisor teeth, however, it agrees perfectly with the animals of that genus.

“This animal was caught in a trap baited with cheese, amongst the bushes at King George’s Sound.”—D.

28. MUS GOULDII.

_M. vellere longo, molli, ochraceo, pilis nigricantibus adsperso, his
ad latera rarioribus: corpore subtùs, pedibusque albis: auribus
majusculis: caudâ, capite corporeque paulo breviore._

DESCRIPTION.—Ears rather large and slightly pointed, tarsi slender and
tolerably long; tail about equal in length to the body and half
the head; fur long and soft; general colour pale ochreous yellow;
on the back there are numerous long black hairs interspersed with
the ordinary fur, which gives a darker hue and somewhat variegated
appearance to that part; feet, chin, throat, and the whole under
parts of the body white; ears brown, sparingly clothed with minute
yellow hairs, both externally (excepting on the forepart, where
they are brownish) and internally; tail brownish above, and
yellowish white beneath; the hairs of the moustaches long, and of
a brown colour; upper incisors deep orange, lower incisors yellow;
claws white. The hair of the back is of a deep lead colour at the
base, pale ochre near the apex, and dusky at the apex; the longer
hairs are black; the hairs of the belly are deep gray at the base
and broadly tipped with white.

In. Lines.
Length from nose to root of tail 4 8
of tail 3 6
from nose to ear 1 0½
of tarsus (claws included) 1 0½
of ear 0 7

VAR. β.—General colour of the fur pale ochreous yellow, the feet,
under side of the tail and the whole of the under parts, as well
as the lower portion of the sides of the body, white; hairs of the
back palish gray at the base, those of the belly indistinctly
tinted with very pale gray at the roots; ears and moustaches pale
brown.

Habitat, New South Wales.

This species is about half-way between _Mus Rattus_ and _Mus musculus_ in size, and is remarkable for its delicate colouring. The molar teeth are figured in Plate 34; fig. 18. _a_, represents the molars of the upper jaw, and fig. 18. _b_, those of the lower.

GENUS—REITHRODON.[25]

_Dentes primores ²⁄₂; inferioribus acutis, gracilibus, et anticè
lævibus; superioribus gracilibus, anticè longitudinalitèr sulcatis._

_Molares utrinque ³⁄₃ radicati; primo maximo, ultimo minimo: primo
superiore plicas vitreas duas externè et internè alternatìm
exhibente; secundo, et tertio, plicas duas externè, internè unam:
primo inferiore plicas vitreas tres externè, duas internè; secundo,
plicas duas externè, unam internè; tertio unam externè et internè,
exhibentibus._

_Artus inæquales: antipedes 4–dactyli, cum pollice exiguo: pedes
postici 5–dactyli, digitis externis et internis brevissimis._

_Ungues parvuli et debiles. Tarsi subtùs pilosi._

_Cauda mediocris, pilis brevibus adpressis instructa._

_Caput magnum, fronte convexo: oculis magnis: auribus mediocribus._

The present genus according to my views belongs to the family _Muridæ_. The modifications of structure which have led me to separate it from the genus _Mus_ are as follows:

_External characters._—The most conspicuous points of distinction
between the external characters of _Reithrodon_ and _Mus_ (if we
regard _M. rattus_, _M. decumanus_ or _M. musculus_ as typical
examples of that genus,) consist in the arched form of the head, the
large size of the eyes, the stout form of the body, and the upper
incisors being grooved. The ears, tail and feet are more densely
clothed with hairs, and the tarsus is covered with hair beneath,—at
least the hinder portion.

_Cranium._—The skulls of the species of the present genus differ from
those of the species of _Mus_ in being proportionately shorter and
broader, and more arched; the facial portion of the skull is larger,
compared with the cranial, the space between the orbits is narrower,
and the orbits are larger; the palate is narrower and the incisive
foramina are more elongated and larger. The pterygoids approximate
anteriorly, so that the posterior _nares_ are greatly contracted. As
in the genus _Mus_ the anterior root of the zygomatic arch is
directed upwards from the plane of the palate, and forwards in the
form of a thin plate, protecting an opening behind, which leads into
the nasal cavity, and also forming the outer boundary both of the
ant-orbital foramen, and a second opening whose outlet is directed
upwards. This thin plate, however, is narrower than is usually found
in the genus _Mus_. The most striking differences observable in the
lower jaw consist in the smaller size of the coronoid process, and
its being curved outwards; the condyloid process is narrower, and
the angle of the jaw, or descending ramus, approaches more nearly to
a quadrate form—the posterior edge of the jaw is more deeply
emarginated.

_Dentition._—The incisors are narrow and compressed as in the genus
_Mus_, but they are less deep from front to back; those of the upper
jaw (Plate 33. fig 2. _b._) have each a distinct longitudinal
groove, which is situated nearer to the outer than to the inner edge
of the tooth. Close to the inner edge of each of these teeth an
indistinct second longitudinal groove may be seen by means of a
lens. The lower incisors are nearly equal in width to the upper.

The crowns of the molar teeth in the young _Reithrodon_ are higher
than in _Mus_, and they are rootless; in the adult animal, however,
they possess distinct roots. The folds of enamel form sigmoid
flexures, are closely approximated to each other, and those of the
opposite sides of the tooth meet.

1. REITHRODON CUNICULOÏDES.
PLATE XXVI.

Reithrodon cuniculoïdes, _Waterh._, Proceedings of the Zoological
Society of London for February 1837, p. 30.

_R. suprà griseus, flavo-lavatus, pilis nigris intermixtis; abdomine
guláque pallidè flavis; natibus albis; pedibus albis; auribus
mediocribus, intùs pilis flavis, extùs pilis pallidè flavis,
obsitis; pone aures, notâ magnâ albescenti-flavâ; caudâ corpore
breviore, suprà pallidè fuscâ, subtùs albâ._

DESCRIPTION.—Head rather large and arched; ears moderate; tail nearly
as long as the body; tarsi rather long; fur long and very soft.
General tint of the upper parts of the body grayish brown, with a
considerable admixture of yellow; of the sides of the body grayish
tinted with yellow; the lower portion of the cheeks, and the lower
half of the sides of the body are of a delicate yellow colour; the
under parts of the head and body are yellowish white; the fore
part of the thighs is whitish; the rump, feet, and tail are white,
excepting the upper surface of the latter, which is brown; behind
each ear there is a patch of yellowish white hairs. The ears are
tolerably well clothed with hairs; those on the inner side are for
the most part of a yellow colour, but towards the posterior margin
they are brown; externally, the hairs are also yellow, excepting
on the fore part, where they are dusky brown. The hairs of the
moustaches are very long and numerous; black at the base, and
grayish at the apex. The feet are well clothed with hairs which
cover and nearly hide the claws; the under side of the tarsus is
clothed with grayish brown hairs. The tail is well clothed with
tolerably long hairs which completely hide the scales. The hairs
on the back are of a deep gray colour at the base, broadly
annulated with yellow near the apex, and dusky at the apex: the
longer hairs are black: on the throat and belly the hairs are deep
gray at the base, and broadly tipped with pale yellow—towards the
cheeks and sides of the body with a deeper yellow. The incisors
are yellow.

In. Lines.
Length from nose to root of tail 6 5
of tail 3 3½
from nose to ear 1 4
of tarsus (claws included) 1 4¼
of ear 0 7

Habitat, Patagonia, (_April and January_).

In the arched form of the head this little animal bears considerable resemblance to a young rabbit, a resemblance which has struck almost all who have seen it, I have therefore applied to it the specific name _Cuniculoïdes_. The skull is figured in Plate 33, fig. 2. _a._, its dimensions are as follows:—

In. Lines. Total length 1 4 Width 0 10 Length of nasal bones 0 7 of incisive foramina 0 4¾ Distance between the outer surface of the incisors and the front molar upper jaw 0 5 Longitudinal extent of the three molars of the upper jaw 0 3¾ Length of a ramus of the lower jaw, without the incisor 0 9¾

The molar teeth of the upper jaw are figured in Plate 33, fig. 2, _c._ and 2, _e_; of the lower jaw, fig. 2, _d_. Fig. 2, _b_, represents the incisors of the upper jaw magnified. Fig. 21, _a_, Plate 34, represents the skull, viewed from beneath, fig. 21, _b_, is the side view of the same, and fig. 21, _c_, is the lower jaw.

“Specimens were procured at Port Desire, St. Julian, and Santa Cruz; at this latter place they were caught in numbers, (in traps baited with cheese,) both near the coast and on the interior plains. A specimen from Santa Cruz weighed 1336 grains. In the early part of January, there were young individuals at Port St. Julian.”—D.

2. REITHRODON TYPICUS.

Reithrodon typicus, _Waterh._, Proceedings of the Zoological Society
of London for February 1837, p. 30.

_R. vellere suprà pilis flavescenti-fuscis et nigrescentibus
intermixtis composito; regione circa oculos, genis, lateribusque
corporis auratis, pilis pallidè fuscis intermixtis; partibus
inferioribus auratis; rhinario ad latera flavescenti-albo; auribus
magnis, intùs pilis flavis, extùs flavis et fuscis, indutis; caudâ
suprà pallidè fuscâ, subtùs sordidè albâ; pedibus albis._

DESCRIPTION.—Ears large; tarsi moderate; fur moderately long; general
tint of the upper parts brown—of the upper surface of the head
blackish; on the cheeks and flanks a rich yellow tint prevails;
the under parts of the head and body are bright yellow; the feet
are white; the tail is brownish above and dirty white beneath. The
ears are tolerably well clothed with hairs, and these are of a
yellowish colour, excepting on the fore part, externally, where
they are brown; the tarsi are covered beneath with grayish brown
hairs; the hairs of the moustaches are numerous and moderately
long, black at the base and grayish at the apex. The hairs of the
back are deep gray at the base, broadly annulated with yellow near
the apex, and black at the apex; on the upper surface of the head
the hairs are very narrowly annulated with yellow, hence a
blackish hue prevails. The longer hairs on the back are black; the
hairs of the throat and belly are gray at the base, and broadly
tipped with yellow. The incisors are yellow.

In. Lines.
Length from nose to root of tail 6 0
of tail ?[26]
from nose to ear 1 4½
of tarsus (claws included) 1 2½
of ear 0 8½

Habitat, Maldonado, La Plata, (_June_).

This species is of a darker colour than the last, its ears are much larger and the tarsi are shorter. It has the same rabbit-like appearance. The molar teeth of the lower jaw are figured in Plate 33, fig. 4, _a_.

“This mouse, when alive, from its very large eyes and ears, had a singular appearance, somewhat resembling that of a little rabbit. It frequents small thickets in the open grassy savannahs near Maldonado, and was caught with facility by means of traps baited with cheese.”—D.

3. REITHRODON CHINCHILLOIDES.
PLATE XXVII.

_R. vellere longissimo et mollissimo; corpore suprà et ad latera
cinereo, flavescenti-fusco lavato, subtùs flavescenti-albo; caudâ
corpore breviore, suprà fuscâ, subtùs albâ: auribus parvulis: tarsis
mediocribus._

DESCRIPTION.—Ears small; tail shorter than the body; tarsus moderate;
fur long and extremely soft. General hue of the upper parts of the
head and body ashy-brown; the lower part of the cheeks and sides
of the body are of a delicate yellow colour; the under parts of
the head and body and the rump are cream colour. The ears are
blackish;[27] the tail is tolerably well clothed with longish
hairs, which are, however, not so thickly set as to hide the
scales—on the upper side they are blackish brown; on the sides and
beneath they are white. The feet are white. All the fur is of a
deep gray colour at the base; the hairs of the back are of a very
pale yellow colour (almost white) near the tip, and brown at the
tip; the longer hairs are black at the apex. The incisors are
yellow; the hairs of the moustaches are numerous and very
long—some of them are whitish, and others are black at the root,
and gray at the apex.

In. Lines.
Length from nose to root of tail 5 0
of tail 2 4
from nose to ear 1 2
of tarsus (claws included) 1 0
of ear 0 5½

Habitat, South shore of the Strait of Magellan, near the Eastern
entrance.

This little animal was preserved in spirit, and has since been mounted, it is probable, therefore, that the colours have been slightly changed. It is of a smaller size than either of the preceding species. Its fur is long, extremely soft, and somewhat resembles that of the Chinchilla. The ears are smaller, and the tail is shorter, and less densely clothed with hairs than in _Reithrodon cuniculoides_. The skull (see Plate 43, fig. 20, _a_, 20, _b_, and 20, _c_,) differs in many respects from that of the species last mentioned. It is of a smaller size, the nasal portion is proportionately shorter and narrower, the incisive foramina are shorter; the pterygoid processes do not approximate so nearly at their base, and the pterygoid fossæ are very shallow, whereas in _R. cuniculoides_ they are deep. In the skull of the animal just mentioned there are two distinct longitudinal grooves on the palate, which extend backwards from the incisive foramina, and terminate in two rather large and deep excavations: these excavations are in the palatine bone, and situated between the last molar teeth; they are separated from each other by a narrow, longitudinal, elevated ridge; a narrow ridge also separates them from the pterygoid fossæ. At the bottom of each of these hollows are several minute foramina, and in front of them there are two larger longitudinal foramina. In _R. chinchilloides_, the longitudinal grooves on the palate and the posterior hollows are shallow, and consequently much less distinct; the pterygoid fossæ are very nearly on the same plane as the palate, and are indicated only by a very slight depression. The incisor teeth are broader than in _R. chinchilloides_, and the molar teeth are proportionately smaller. The thin plate which forms the anterior root of the zygomatic arch is deeply emarginated in front in _R. cuniculoides_ (see Plate 34, fig. 21, _b._); but in _R. chinchilloides_, the anterior margin of this plate is nearly straight, (see Plate 34, fig. 20, _c._)

In the form of the lower jaw of the two animals under consideration there are differences which will be more clearly understood upon comparing the figures. I will therefore merely notice one remarkable character which is found in _R. cuniculoides_, and that is, that the condyloid process is rather deeply concave on the inner side, a character which does not exist in _R. chinchilloides_, nor do I recollect having observed it in any other Rodent.

The principal dimensions of the skull of _R. chinchilloides_, are as follows:—

In. Lines. Total length 1 2 Width 0 8½ Length of nasal bones 0 6⅓ of incisive foramina 0 4 Distance between the outer surface of the incisors and the first molar tooth, upper jaw 0 4½ Longitudinal extent of the three molars of the upper jaw, taken together 0 2¾ Length of a ramus of the lower jaw without the incisor 0 8

_General Observations upon the foregoing Species of Muridæ._

In the foregoing descriptions I have endeavoured to convey an idea of the characters of the species of mice submitted to me for examination and description, by Mr. Darwin: there are, however, some points upon which I have been silent in my descriptions. I allude to the characters observable in the dentition. I have omitted to notice the various modifications in the structure of the molar teeth, because I found it would lengthen the descriptions to no good purpose, inasmuch as of almost all the species I have made outlines of the molars, which will convey a more clear idea than any verbal description can do.

Upon an inspection of the Plates, it will be seen, that by far the greater portion of the teeth figured, may be referred to one particular type of form or pattern, and that this pattern does not agree with that observed in the molars of _Mus Rattus_, _M. decumanus_, or _M. musculus_, whilst these three species agree essentially with each other.

In the young Black Rat (_Mus Rattus_), before the teeth are worn, the two anterior molar teeth, on either side of the upper jaw, present three longitudinal rows of tubercles, a central series of larger tubercles, and on each side of these, a row of smaller ones. The front molar has three of the larger tubercles arranged along the middle of the tooth; three smaller ones on the outer side, and two, on the inner side. The second molars have two central tubercles, two outer, and two inner ones. The posterior molar is nearly round, the body of the tooth consists of three principal tubercles, and one small tubercle, situated on the inner and anterior portion of the tooth.

The corresponding teeth in the young of _Mus bimaculatus_ present a very different appearance; the molars, instead of having three longitudinal rows of tubercles, have only two. An idea of the appearance of these teeth may be formed by removing the inner row of tubercles from the molars of _Mus rattus_. We should then have, as in _Mus bimaculatus_, molars of a narrower form, the first tooth presenting six tubercles, the second, four; and the posterior tooth devoid of the small inner lobe; the opposing tubercles of each tooth, however, in _M. bimaculatus_, are of equal size.

The molars of the lower jaw of _Mus bimaculatus_ agree with those of _M. Rattus_ as to the number of tubercles which they possess; they are, however, proportionately longer and narrower, and, when a little worn, these teeth, as well as those of the upper jaw, differ considerably from those of _M. Rattus_. In the last named animal, when the molars are slightly worn, the ridges of enamel run completely across the tooth, as in Figs. 18 and 19, Plate 34. Such is not the case in _M. bimaculatus_ at any age. As soon as the molar teeth are worn, the folds of enamel penetrate the body of the tooth on each side, and those of one side alternate with those of the other,—in fact, they very nearly resemble those of the _Hamsters_ (_Cricetus_).

I have selected the molar teeth of _Mus Rattus_ and _M. bimaculatus_ for comparison, since I happened to possess specimens displaying both the young and adult states of each. But had I selected, on the one hand, almost any of the species brought from South America by Mr. Darwin, and, on the other hand, the _Mus musculus_ or _M. decumanus_, I should have had to point out the same distinctions—the former agreeing in dentition with _M. bimaculatus_, and the latter with _M. Rattus_.

The differences pointed out, between the molar teeth of _Mus Rattus_ and those of _M. bimaculatus_, I cannot but consider as important, since all the Old World species of _Mus_ which I have yet had an opportunity of examining (and they are numerous) agree essentially with the former, whilst the only _Mus_ from S. America (excepting _M. Musculus_ and _M. decumanus_, which are carried in ships to all parts of the world) in which I have as yet found molar teeth like those of _M. Rattus_, is the _Mus Maurus_, and this it has been stated is possibly a variety of _M. decumanus_.

Although as yet I have not met with species in the Old World possessing the characters of the South American _Muridæ_, among those of North America, several have come under my observation. The _Mus leucopus_, _Symidon hispidum_, and the species of _Neotoma_ certainly belong to the same group,[28] as does also the species of the Galapagos Islands, described in this work under the name _Galapagoensis_.

These considerations have induced me to separate the South American mice from those of the Old World,—or rather from that group of which _M. decumanus_ may be regarded as the type,—and to place them, together with such North American species as agree with them in dentition, in a new genus bearing the name _Hesperomys_.[29]

Whether this group be confined to the Western hemisphere or not, I will not venture to say, but I think I may safely affirm that that portion of the globe is their chief metropolis.

The species of the genus _Hesperomys_, which depart most from the type—whose dentition is least like figs. 5, _a_, and 5, _b_, Plate 33., or 6, _a_, and 6, _b_, of the same Plate—recede still farther from the genus _Mus_, and approach more nearly (as regards the dentition) to the _Arvicolidæ_. Among the species here described I may mention as examples, _M. griseo-flavus_, _M. zanthopygus_, and _M. Darwinii_;—see the molar teeth figured in Plate 34. figs. 15, 16, and 17,—and among the North American species, those constituting the genus _Neotoma_. The latter make by far the nearest approach to the _Arvicolidæ_ of any which have yet come under my observation, not only in the dentition, but in the form of the skull and the large size of the coronoid process of the lower jaw; there is, nevertheless, a tolerably well marked line of distinction between the crania of the _Arvicolidæ_ and _Neotoma_.

The skulls of the animals belonging to the genera _Castor_, _Ondatra_, _Arvicola_, _Spalax_, and _Geomys_, which constitute the principal groups of the family _Arvicolidæ_, when compared with those of the family _Muridæ_, present, among others, the following distinctive characters.

The temporal _fossæ_ are always much contracted posteriorly, by the great anterior and lateral development of the temporal bones; the plane of the intermolar portion of the palate is below the level of the anterior portion; the coronoid process of the lower jaw is very large, the articular portion of the condyloid process is proportionately broad; the descending ramus, or posterior coronoid process, is so situated that its upper portion terminates considerably above the level of the crowns of the molars; this same process is generally[30] directed outwards from the plane of the horizontal ramus. The incisor teeth of the _Arvicolidæ_ differ from those of the _Muridæ_ in being proportionately broader and less deep from front to back—they are not laterally compressed as in _Mus_. The molar teeth are rootless,[31] and the folds of enamel are the same throughout the whole length of the tooth; whereas in _Mus_ they enter less and less deeply into the body of the tooth as we recede from the crown, and towards the base of the visible portion (the tooth being in its socket) the indentations of the enamel are obliterated.

Now in the species of _Hesperomys_, the molar teeth are always rooted, and in the form of the skull and the lower jaw they agree with the _Muridæ_, and do not present the characters above pointed out as distinguishing the _Arvicolidæ_, and as regards the cranium and lower jaw, it is only in the genus _Neotoma_ that any approach is evinced.

Of the various groups of the order _Rodentia_ found in South America, the _Sciuridæ_, so far as I am aware, are chiefly confined to the more northern parts, and do not occur in the most southern; the _Myoxidæ_, _Gerboidæ_, and _Arvicolidæ_ are wanting. The species of the family _Muridæ_ belong to different sections to those of the Old World. Of the _Leporidæ_ I am acquainted only with one well established species—the _Lepus Braziliensis_, which however is not found “in tota America Australi,” as Fischer says, there being no Hare yet found in the more southern parts, where the _Cavies_ and _Chinchillas_ appear to take their place. The remaining South American Rodents—certain species of _Hystricidæ_, the genera, _Echimys_, _Dasyprocta_, _Cælogenys_ and _Myopotamus_, together with the _Octodontidæ_ and _Chinchillidæ_, all possess a peculiar form of skull and of the lower jaw, (more or less approaching to figs. 1, Plate 33, and figs. 23, Plate 34.) which I have described in the “Magazine of Natural History,” for February 1839, and which is rarely found in the North American, or Old World Rodents. In enumerating the above groups, I omitted the _Caviidæ_, because in the form of the lower jaw they differ somewhat from the rest—they possess, in fact, a form of lower jaw peculiar to themselves; but in the Chinchillas[32] the transitions between one form and the other are found.

The South American _Muridæ_, which form the chief part of Mr. Darwin’s collection, were none of them procured further north than latitude 30°, with the exception of those from the Galapagos Archipelago. The species occur at the following localities.

WEST COAST OF SOUTH AMERICA.

GALAPAGOS ARCHIPELAGO.

Mus Jacobiæ.
—— Galapagoensis.

COQUIMBO.

Mus longipilis.
—— Renggeri.
—— Darwinii.

VALPARAISO.

Mus Renggeri.
—— _decumanus_.

CONCEPCION.

Mus longicaudatus.

CHILOE AND CHONOS ARCHIPELAGO.

Mus brachiotis.

EAST COAST OF SOUTH AMERICA.

MALDONADO.

Mus _decumanus_.
—— maurus.
—— _Musculus_.
—— tumidus.
—— nasutus.
—— obscurus.
—— arenicola.
—— bimaculatus.
—— flavescens.
Reithrodon typicus.

BUENOS AYRES.

—— Mus _decumanus_.

BAHIA BLANCA.

Mus Braziliensis.
—— elegans.
—— gracilipes.

RIO NEGRO.

Mus griseo-flavus.

PORT DESIRE.

Mus canescens.

ST. JULIAN.

Reithrodon cuniculoïdes.
—— xanthopygus.
Reithrodon cuniculoïdes.

SANTA CRUZ.

Mus canescens.
—— micropus.
—— xanthopygus.
Reithrodon cuniculoïdes.

FALKLAND ISLANDS.

Mus _decumanus_.
—— _Musculus_.

STRAITS OF MAGELLAN.

Mus xanthorhinus.
—— Magellanicus.
Reithrodon chinchilloïdes.

SECTION—HYSTRICINA.
FAMILY— ——?

MYOPOTAMUS COYPUS.
Myopotamus Coypus, _Auct._

“This animal, in Chile, is known by the name of “Coypu;” at Buenos Ayres, where an extensive trade is carried on with their skins, they are improperly called ‘nutrias,’ or otters. In Paraguay, according to Azara, their Indian name is ‘guiya.’ On the east side of the continent they range from Lat. 24° (Azara) to the Rio Chupat in 43° 20′;—distance of 1160 miles. This latter river is 170 miles south of the Rio Negro, and the intervening space consists of level, extremely arid, and almost desert plains, with no water, or at most one or two small wells. As the Coypu is supposed never to leave the banks of the rivers, and being, from its web-feet and general form of body, badly adapted for travelling on land, its occurrence in this river is a case, like so many others in the geographical distribution of animals, of very difficult explanation. The same remark is indeed applicable, but with less force, to its existence in the Rio Negro. On the west coast, it is found from the valleys of central Chile (Lat. 33) to 48° S., or perhaps even somewhat farther, but not in Tierra del Fuego. So that, on the Atlantic side of the continent, the plains of Patagonia check its range southward, as, on the Pacific side, the deserts of Chile do to the north. Its range, including both sides, is from 24° to 48°, or 1440 miles. In the Chonos Archipelago these animals, instead of inhabiting fresh water, live exclusively in the bays and channels which extend between the innumerable small islets of that group. They make their burrows within the forest, a little way above the rocky beaches. I believe it is far from being a common occurrence, that the same species of any animal should haunt indifferently fresh water, and that of the open sea. We shall see that the Capybara is sometimes found on the islands near the mouth of the Plata; but these cannot be considered as their habitual station in the same manner as the channels in the Chonos Archipelago are to the Coypu. The inhabitants of Chiloe, who sometimes visit this Archipelago for the purpose of fishing, state that these animals do not live solely on vegetable matter, as is the case with those inhabiting rivers, but that they sometimes eat shell-fish. The Coypu is said to be a bold animal, and to fight fiercely with the dogs employed in chasing it. Its flesh when cooked is white and good to eat. An old female procured (January) amongst these islands, weighed between ten and eleven pounds.” D.

FAMILY—OCTODONTIDÆ.

CTENOMYS BRAZILIENSIS.

Ctenomys Braziliensis, _De Blainville_, Bulletin de la Société
Philomatique, June 1836, p. 62.

Maldonado, La Plata, (_June_.)

“This animal is known by the name of Tucutuco. I have given an account of its habits in my journal, but I shall here repeat it for the sake of keeping together my observations on the less known animals. The Tucutuco is exceedingly abundant in the neighbourhood of Maldonado, but it is difficult to be procured, and still more difficult to be seen, when at liberty. Azara,[33] who has given an account of its habits, with which every thing I saw perfectly agrees, states that he never was able to catch more than one, although they are so extremely common. The Tucutuco lives almost entirely under ground, and prefers a sandy soil with a gentle inclination; but it sometimes frequents damp places, even on the borders of lakes. The burrows are said not to be deep, but of great length. They are seldom open; the earth being thrown up at the mouth into hillocks not quite so large as those made by the mole. Considerable tracts of country are completely undermined by these animals. They appear, to a certain degree, to be gregarious; for the man who procured my specimens had caught six together, and he said this was a common occurrence. They are nocturnal in their habits; and their principal food is afforded by the roots of plants, which is the object of their extensive and superficial burrows. In the stomach of one which I opened I could only distinguish, amidst a yellowish green soft mass, a few vegetable fibres. Azara states that they lay up magazines of food within their burrows.

“The Tucutuco is universally known by a very peculiar noise, which it makes when beneath the ground. A person, the first time he hears it, is much surprised, for it is not easy to tell whence it comes, nor is it possible to guess what kind of creature utters it. The noise consists in a short, but not rough, nasal grunt, which is repeated about four times in quick succession; the first grunt is not so loud, but a little longer, and more distinct than the three following: the musical time of the whole is constant, as often as it is uttered. The name Tucutuco is given in imitation of the sound. In all times of the day, where this animal is abundant, the noise may be heard, and sometimes directly beneath one’s feet. When kept in a room, the Tucutucos move both slowly and clumsily, which appears owing to the outward action of their hind legs; and they are likewise quite incapable of jumping even the smallest vertical height. Mr. Reid, who dissected a specimen which I brought home in spirits, informs me that the socket of the thigh-bone is not attached by a ligamentum teres; and this explains, in a satisfactory manner, the awkward movements of their hinder extremities. Their teeth are of a bright wax yellow, and are never covered by the lips: they are not adapted to gnaw holes or cut wood. When eating any thing, for instance biscuit, they rested on their hind legs and held the piece in their fore paws; they appeared also to wish to drag it into some corner. They were very stupid in making any attempt to escape; when angry or frightened, they uttered the Tucutuco. Of those I kept alive, several, even the first day, were quite tame, not attempting to bite or to run away; others were a little wilder. The man who caught them asserted that very many are invariably found blind. A specimen which I preserved in spirits was in this state; Mr. Reid considers it to be the effect of inflammation in the nictitating membrane. When the animal was alive, I placed my finger within half an inch of its head, but not the slightest notice was taken of it: it made its way, however, about the room nearly as well as the others. Considering the subterranean habits of the Tucutuco, the blindness, though so frequent, cannot be a very serious evil; yet it appears strange that any animal should possess an organ constantly subject to injury. The mole, whose habits in nearly every respect, excepting in the kind of food, are so similar, has an extremely small and protected eye, which, although possessing a limited vision, at once seems adapted to its manner of life.

“Several species probably will be found to exist south of the Plata. At Bahia Blanca (Lat. 39°) an animal burrows under ground in the same manner as the _C. Braziliensis_, and its noise is of the same general character, but instead of being double and repeated twice at short intervals, it is single and is uttered either at equal intervals, or in an accelerating order. I was assured by the inhabitants that these animals are of various colours, and, therefore, I presume that the two kinds of noises proceeded from two species. However this may be, they are extraordinarily numerous: many square leagues of country between the Sierras Ventana and Guetru-heigue are so completely undermined by their burrows, that horses in passing over the plain, sink, almost every step, fetlock deep. At the Rio Negro (Lat. 41°) some closely allied (or same?) species utters a noise, which is repeated only twice, instead of three or four times as with the La Plata kind. The sound is, moreover, louder and more sonorous; and so closely resembles that made in cutting down a small tree with an axe, that I have occasionally remained in doubt for some time to which cause to attribute it. Where the plains of Patagonia are very gravelly (as at Port Desire and St. Julian) the Ctenomys, I believe, does not occur; but at Cape Negro, in the Strait of Magellan, where the soil is damper and more sandy, the whole plain is studded with the little hillocks, thrown up by this destructive animal. It occurs likewise south of the Strait, on the eastern side of Tierra del Fuego, where the land is level. Captain King brought home a specimen from the northern side of the Strait, which Mr. Bennett[34] has called _C. Magellanicus_: it is of a different colour from the _C. Braziliensis_. I unfortunately did not make any note regarding the noise of this southern species: but the circumstance of its existence rather corroborates my belief in there being several other kinds in the neighbourhood of the Rio Negro and Bahia Blanca. Otherwise we must believe that the same animal utters different kinds of noises, in different districts; a fact which I should feel much inclined to doubt.

“Azara[35] says that the Tucutuco may he ‘found every where; provided that the soil be pure sand, and the situation not subject to be overflowed. As these conditions are fulfilled only in certain spots, their warrens are far separated from each other, even sometimes more than twenty-five leagues, without it being possible to conceive how these animals have been able to pass from one place to another.’ The difficulty, I think, is much overstated; for, as I have said, the burrows of the Tucutuco are sometimes made in very damp places, near lakes; so that they certainly might pass over almost any kind of country. But if the _C. Braziliensis_ and _C. Magellanicus_ be considered as one species, as some French authors are inclined to do, then the difficulty will be increased in a very remarkable manner, as we shall be obliged to transport the Tucutuco over wide plains of shingle, and across many great rivers, and an arm of the sea.”—D.

POEPHAGOMYS ATER.

Poephagomys ater, _F. Cuvier_, Annales des Sciences Naturelles, 2d
series, Zoologie, tom. 1. p. 321. June, 1834.

Chile, (_September_.)

“This animal is generally scarce, but in certain districts, I believe, of an alpine character, it is abundant. It excavates very extensive superficial burrows, no doubt, for the purpose of feeding on the roots of plants, as in the case of the _Ctenomys Braziliensis_, the habits of which have just been described. Horses passing over districts frequented by these animals, sink fetlock deep through the turf. I procured my specimen from Valparaiso, where the country-people called it ‘Cururo.’”—D.

OCTODON CUMINGII.

Octodon Cumingii, _Bennett_, Proc. of Committee of Science and
Correspondence of the Zool. Soc. for 1832, p. 46.

—— —— Transactions of the Zoological Society of London, vol. ii. p.
81. Pl. 16.

Dendrobius Degus, _Meyen_. Acta Academiæ, c. 1. c. Naturæ Curiosorum,
xvi. p. 610. Pl. 44, 1833.

Valparaiso, Chile, (_October_.)

These little animals are exceedingly numerous in the central parts of Chile. They frequent by hundreds the hedge-rows and thickets, where they make burrows close together, leading one into another. They feed by day in a fearless manner; and are very destructive to fields of young corn; when disturbed, they all run together towards their burrows in the same manner that rabbits in England do when feeding outside a covert. When running they carry their tails high up, more like squirrels than rats; and they often remain seated on their haunches, like the former animals. According to Molina[36] they lay up a store of food for the winter, but do not become dormant. The Octodon is the “degu” of that author: he says that the Indians in past times used to eat them with much relish. These animals appear to be very subject to be piebald and albinos; as if partly under the influence of domestication.

GENUS—ABROCOMA.[37]