Part 16

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