The two species included in this genus are intermediate between the Mouse-Lemurs and the Dwarf-Lemurs, and are really more nearly related to the former than to the latter. The skull is flat and depressed as in _Chirogale_, and the brain-case small and almost vertical behind. The posterior foramina in the palate are small. In respect to their dentition, the cusps of the upper molars are blunter and shorter than in the Mouse-Lemurs, but less so than among the Dwarf-Lemurs; the hind inner cusps of the anterior and median molars are large, and the ridge from the inner cusp is less intimately joined to the two outer cusps than in the Dwarf-Lemurs. I. SAMAT'S FAT-TAILED LEMUR. OPOLEMUR SAMATI. _Chirogalus samatii_, Grandid., Rev. et Mag. de Zool., xx., p. 49 (1868). _Opolemur milii_, Gray, P. Z. S., 1872, pp. 853-4, pl. lxx., fig. i. (in part). _Opolemur samati_, Forsyth Major, Nov. Zool., vol. i., p. 18 (1894). CHARACTERS.--Head, Cat-like; hair on body and tail very short, longer at tip of tail; tail very thick at base, from accumulation of fat, especially in the month of August. Length, 7½ inches; tail, 6½. Fur above dark grey, washed with ferruginous, the tips of the hairs silvery-grey; tail faded rufous; a white spot on the forehead, becoming a line down the centre of the nose; a black circle round the eyes; ears slightly longer; tail shorter {63}and thicker proportionately than in _Chirogale milii_; under surface and inner side of limbs fulvous. DISTRIBUTION.--This species, according to M. Grandidier, to whom all our knowledge of it is due, has been obtained on the River Tsidsibon, but is reported from other places on the west coast of Madagascar. II. THOMAS' FAT-TAILED LEMUR. OPOLEMUR THOMASI. _Opolemur thomasi_, Forsyth Major, Nov. Zool., vol. i., p. 20, Taf. i., fig. 1 Taf., ii., figs. 2 and 11 (1894). CHARACTERS.--Nearly allied to _O. samati_. Head broad, flat; snout short; ears short. Above grey, with a wash of rusty brown, the tips of the hair glistening silvery-grey; top of head somewhat darker; under side of tail lighter; a white band between the eyes extending down to the nose-pad, which is naked; round the neck a white ring broken by a grey spot; ring round the eyes, and hair of ears, brownish-black; cheeks, lips, chin, throat, breast, belly, inner side of limbs, upper side of hands and feet, yellowish-white, and inclining to greyish-white, where it merges into the upper side. Length, 9¼ inches; tail, 8 inches. Skull depressed; brain-case flat and short; facial portion blunt; inter-parietal bone broad and short. Posterior upper pre-molar broader than the median, and broader than the same tooth in _O. samati_, the median pre-molar lacking the inner cusp. Nasal bones sharply keeled in the mid-line. DISTRIBUTION.--Of this species only the three specimens, in the British Museum, are yet known. They were obtained near Fort Dauphin, on the south-east coast of Madagascar.