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._