As I wrote my paper on Sciurus (Rheithrosciurus) microtis, see Notes from the Leyden Museum, Part I, 1879, p. 40, I knew Rheithrosciurus macrotis only from the both short annotations of the late Gray about that Squirrel. I here verbally copie his descriptions: Proc. Zool. Soc. Lond. 1856, p. 341, pl. XLVI, he writes: »Among the specimens of animals which the British Museum has lately received from Mr. Wallace from Sarawak, is a large, well-marked species of Squirrel, particular for having very large, longish pencilled ears like the European species, with a broad white streak on the upper part of each side, and a very broad full tail, grisled, with large white tips to the hairs. Sciurus macrotis. Ears large, with large pencil of elongate hairs. Dark chestnut-brown, very minutely grisled with pale tips to the hairs. Rump, outside of thighs and base of tail redder; point of thighs bright bay; feet blackish; upper part of the side with a broad pale streak; cheeks and inner side of legs paler; chin, throat, and beneath white; tail very broad, with very long white-tipped hairs. Length 13, tail 11 = 24 inches. Hab. Sarawak (Mr. Wallace).” — and: Ann. and Mag. of Nat. Hist. 1867, p. 271, we read: »The front edge of the cutting-teeth broad, rounded, closely longitudinally grooved. Rheithrosciurus nov. gen. Head large, compressed, short; ears large, with a pencil of elongated hairs at the tip; cutting-teeth broad, rounded in front and closely longitudinally grooved. The limbs free; feet large, strong. Tail as long as the body and head, very thick, clavate, covered with long flaccid hairs. The grooving of the teeth is a pecularity not observed in any other Sciuridae. Rheithrosciurus macrotis. Brown, very minutely punctulated; throat and beneath white; lateral streaks broad, yellowish; front of thighs bay. Tail blackish, whitish washed. Hab. Sarawak (Wallace). Type in B. M.” — In my above mentioned paper I already briefly showed that these descriptions are highly short and that they do not agree the one with the other. As I often before had seen Squirrels with grooved upper cutting-teeth, that is to say, where those teeth are provided each with one or two grooves and while Gray in his first description entirely had overlooked this character, I thought that his words »cutting-teeth closely longitudinally grooved” in his second note should be understood as only relating the upper ones, for squirrels with grooved lower cutting-teeth were not known. In my opinion now the grooving of the upper cutting-teeth in squirrels has no generic value, but my Saleyer squirrel presenting that character, I placed the latter in the neighborhood of Gray’s squirrel, but with Gray’s generic title Rheithrosciurus in Parenthesi. In doing so I only intented to fix the attention of the readers on the always excellent character of the grooved cuttingteeth in distinguishing species. Anderson in his »Yunnan-Expedition” says not a single word about the grooved character of the incisors, and he describes the squirrel as follows: »The head is large, compressed and short. The ears are large with a pencil of elongated hairs at their tips, the feet are large and strong and the sides of the animal are laterally banded. The general colour of the animal is dark-nutbrown, very minutely punctulated; the hind quarter, including the base of the tail and the outside of the fore- and hindlimbs bright bay; the feet blackish. There is a brownish band from the axilla to the groin, with a yellowish white band about it. The cheeks and inner sides of the limbs are pale brownish, grizzled and with long white tips to the hairs. Habitat. Sarawak. Borneo.” Afterwards my friend Trouessart in his Catalogue des Mammifères vivants et fossiles 1880 p. 69 (12), united my microtis with Gray’s macrotis in the genus Rheithrosciurus Thereupon I wrote to Trouessart that I did not accept that genus, as there were still more squirrels which show the same character, but for the rest belong to the most different groups and I shortly explained why I had placed my squirrel in the neighborhood of Gray’s species. But I hardly can express my astonishment as I saw in the Paris Museum and afterwards in the British Museum specimens of Rheithrosciurus macrotis! Indeed it is the most splendid squirrel that I ever saw. The coloring of the body generally resembles that of Sciurus prevostii: like in that species each side is ornated with a broad white band. But the ears are longer than in any other squirrel, viz: 30 mm., they are embellished with a very long tuft measuring 45 mm., the whole ear with pencil also measures about 75 mm. The tail is very bushy and resembles that organ in Chirormjs madagascariensis; its length is about 280 mm. without tuft, while it measures the tuft included 292 mm., also much longer than the body (c. f. Gray’s measures above given), which measures the head included 235 mm. The hairs of the tail are long 92 mm., so that, if the hairs are spread out, the tail has a diameter of about 185 mm.