“Inhabits dry stony places.”—D. 26. MUS GALAPAGOENSIS. PLATE XXIV. _M. suprà fuscus, flavo-lavatus, ad latera flavescens, subtùs albus: pedibus pilis sordidè albis tectis: auribus mediocribus; caudâ, quoad longitudinem, caput corpusque ferè æquante: vellere longo._ DESCRIPTION.—Ears moderate, slightly pointed; tarsi moderate; tail slender, nearly as long as the head and body; fur long, and not very soft; upper parts of the body of a brownish hue, a tint produced by the admixture of black and palish yellow hairs; on the sides of the body the longer black hairs are less abundant, and the prevailing colour is yellow; under parts of the body white, with a very faint yellow tint; feet furnished above with dirty white hairs; ears rather sparingly clothed with hairs, those on the inner side of a yellow colour, and those on the outer side dusky; tail above brown, and beneath whitish; the hairs of the moustaches black; the incisors deep yellow; the hairs on the back are deep gray at the base, broadly annulated with palish yellow near the apex, and blackish at the apex; the longer hairs black; on the belly the hairs are gray at the base, and broadly tipped with yellowish white. In. Lines. Length from nose to root of tail 6 0 of tail 4 9 from nose to ear 1 3¾ of tarsus (claws included) 1 2 of ear 0 7 Habitat, Chatham Island, Galapagos Archipelago, Pacific Ocean, (_October_.) This species is less than _Mus Rattus_. The upper parts of the body have a slightly variegated appearance. The skull of _Mus Galapagoensis_ (Plate 33, fig. 8, _a_,) is rather smaller than that of _M. Rattus_, the nasal portion is proportionately longer, the cranial shorter, and the interparietal bone is smaller, especially in antero-posterior extent; its length is 15 lines, and its breadth is 8⅛ lines. The lower jaw is figured in Plate 34, fig. 14, _a_. Fig. 8, _b_, of Plate 33, represents the molars of the upper jaw, and fig. 8, _c_, those of the lower jaw. “This mouse or rat is abundant in Chatham Island, one of the Galapagos Archipelago. I could not find it on any other island of the group. It frequents the bushes, which sparingly cover the rugged streams of basaltic lava, near the coast, where there is no fresh water, and where the land is extremely sterile.”—D. 27. MUS FUSCIPES. PLATE XXV.