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.