_Measurements._--External measurements of type: total length 229; head and body 140; tail vertebræ 89; hind foot 36 (33.7); ear from meatus 12; ear from crown 7. A second specimen from the type locality gives precisely the same measurements. Cranial measurements of type: greatest length 38 (36);[18] basal length 33 (31); basilar length 30 (29); palatal length 17 (16); greatest length of nasals 11 (10); greatest width of both nasals together 5 (5); interorbital breadth 12 (11.4); zygomatic breadth 22.4 (20); mastoid breadth 17 (16.6); depth of braincase at anterior edge of basi-occipital 13.6 (13); mandible 23 (22); maxillary toothrow (alveoli) 6.4 (7); mandibular toothrow (alveoli) 7 (7). _Specimens examined._--Two, both from the type locality. _Remarks._--While _Sciurus lingungensis_ is scarcely distinguishable from _S. natunensis_ by external characters alone, size of the skull and form of the audital bullæ are clearly diagnostic. Both species from the Natunas are separated from the Bornean _S. lowi_ Thomas by their well developed ears, and shorter broader rostral portion of skull. SCIURUS LUTESCENS sp. nov. 1894. _Sciurus notatus_ THOMAS and HARTERT, Novitates Zoologicæ, I, p. 659. September, 1894 (part, specimens from Sirhassen). _Type._--Adult male (skin and skull) No. 104668 U. S. National Museum. Collected on Sirhassen Island, South Natunas, June 3, 1900. Original number 429. _Characters._--Allied to _Sciurus notatus_, but considerably smaller than the Bornean representative of the species. Colors very pale, the under parts buff or cream-buff (Ridgway, pl. v, nos. 13 and 11) irregularly tinged with gray. _Color._--Entire dorsal surface of body and tail a fine grizzle of black and cream-buff, the individual hairs black with two or three cream buff rings. On tail the grizzle is less fine than on back, and it shows a faint tendency to resolve itself into obscure cross bands. On sides of body and on head the cream-buff brightens to buff. Cheeks and muzzle buff, scarcely grizzled. Feet slightly yellower than sides, under parts and inner surface of legs pale buff, palest anteriorly and laterally (where it about matches the cream-buff of Ridgway) brightest along median line. Under side of tail dull ochraceous-buff slightly grizzled with black. Pencil not different from rest of tail. Between the colors of sides and belly are the usual longitudinal stripes. The outer of these is about 5 mm. in width, and cream-buff in color. The inner is about twice as wide, and black, but much obscured by a thick sprinkling of bluish gray hairs. Outer surface of ears concolor with neck, inner surface like cheeks. The sprinkling of bluish gray hairs on sides of belly extends irregularly forward to axilla and inner side of front leg, occasionally to throat and chin.