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.