DESCRIPTION.—Ears rather large and slightly pointed, tarsi slender and tolerably long; tail about equal in length to the body and half the head; fur long and soft; general colour pale ochreous yellow; on the back there are numerous long black hairs interspersed with the ordinary fur, which gives a darker hue and somewhat variegated appearance to that part; feet, chin, throat, and the whole under parts of the body white; ears brown, sparingly clothed with minute yellow hairs, both externally (excepting on the forepart, where they are brownish) and internally; tail brownish above, and yellowish white beneath; the hairs of the moustaches long, and of a brown colour; upper incisors deep orange, lower incisors yellow; claws white. The hair of the back is of a deep lead colour at the base, pale ochre near the apex, and dusky at the apex; the longer hairs are black; the hairs of the belly are deep gray at the base and broadly tipped with white. In. Lines. Length from nose to root of tail 4 8 of tail 3 6 from nose to ear 1 0½ of tarsus (claws included) 1 0½ of ear 0 7 VAR. β.—General colour of the fur pale ochreous yellow, the feet, under side of the tail and the whole of the under parts, as well as the lower portion of the sides of the body, white; hairs of the back palish gray at the base, those of the belly indistinctly tinted with very pale gray at the roots; ears and moustaches pale brown. Habitat, New South Wales. This species is about half-way between _Mus Rattus_ and _Mus musculus_ in size, and is remarkable for its delicate colouring. The molar teeth are figured in Plate 34; fig. 18. _a_, represents the molars of the upper jaw, and fig. 18. _b_, those of the lower. GENUS—REITHRODON.[25] _Dentes primores ²⁄₂; inferioribus acutis, gracilibus, et anticè lævibus; superioribus gracilibus, anticè longitudinalitèr sulcatis._ _Molares utrinque ³⁄₃ radicati; primo maximo, ultimo minimo: primo superiore plicas vitreas duas externè et internè alternatìm exhibente; secundo, et tertio, plicas duas externè, internè unam: primo inferiore plicas vitreas tres externè, duas internè; secundo, plicas duas externè, unam internè; tertio unam externè et internè, exhibentibus._ _Artus inæquales: antipedes 4–dactyli, cum pollice exiguo: pedes postici 5–dactyli, digitis externis et internis brevissimis._ _Ungues parvuli et debiles. Tarsi subtùs pilosi._ _Cauda mediocris, pilis brevibus adpressis instructa._