DESCRIPTION.—Fur moderate; ears moderate; tail shorter than the body; general colour gray washed with yellow; under parts grayish white. On the upper parts and sides of the head and body the hairs are gray, broadly annulated with yellow near the apex, and dusky at the apex; the mixture producing a yellowish gray tint, approaching somewhat towards olive:—the hairs on the under parts of the body and throat are deep gray at the base, and white at the apex; the hairs of the feet are brownish-white. The tail is tolerably well clothed with hairs; those on the upper surface are brown, and those on the under are dirty white. The ears are well clothed, both externally and internally, with hairs of the same colour as those on the upper parts of the body. The hairs of the moustaches are for the most part whitish, and black at the base. The upper incisors are pale yellow, and the lower incisors are yellowish white. In. Lines. Length from nose to the root of tail 5 1 of tail 2 8 from nose to base of ears 1 2 of tarsus (claws included) 0 11 of ear. 0 5 Habitat, Valparaiso (_August and September_,) Coquimbo (_May_.) Subsequent to the description of this species, under the name of _M. olivaceus_ in the Zoological Society’s Proceedings, I have imagined that perhaps that name might mislead as regards the colouring of the animal;—it certainly has a slight olive hue, but it is not very evident. I have therefore changed the name, and substituted that of the author of the “Naturgeschichte der Säugethiere von Paraguay,” &c. In the collection there are three specimens of the present species; in one of these the hairs of the upper part and sides of the body are annulated with yellowish white, instead of yellow; hence the general hue of these parts is nearly gray. _Mus Renggeri_ is larger than _Mus Musculus_, and much stouter in its proportions; the fur is shorter, much less dense, and less soft than in _Mus brachiotis_. “It inhabits dry stony places, where only a few thickets grow.”—D. 15. MUS OBSCURUS. PLATE XV.—Fig. 2. Mus obscurus, _Waterh._, Proceedings of the Zoological Society of London for February 1837, p. 16. _M. suprà fusco-nigrescens, subtùs flavescens; pedibus obscurè fuscis; unguibus longiusculis; auribus mediocribus; caudâ corpore breviore, suprà nigrescente, subtùs sordidè albâ; vellere mediocri, molli._