_Characters._--Externally like _Ratufa anambæ_ and _R. melanopepla_. Skull about equal to that of latter in length, but conspicuously narrower. _Color._--As the color is precisely like that of _Ratufa anambæ_ and _R. melanopepla_ it requires no description. _Skull and teeth._--The skull is immediately recognizable by its general narrowness, but particularly in the region of the anterior zygomatic roots. Ratio of lachrymal breadth to greatest length, 39. In the other black backed species it is about 42. Audital bullæ narrower and more elongate than in _R. melanopepla_, and more elevated above level of basi-occipital (when skull is held upside down). Lateral processes of basi-occipital obsolete. Teeth as in the related species. _Measurements._--External measurements of type: total length 748; head and body 342; tail vertebræ 406; hind foot 79 (74). Cranial measurements of type: greatest length 48.6 (70);[21] basal length 57 (59); basilar length 52 (53); diastema 15.6 (16); length of nasals 22 (23.4); breadth of nasals anteriorly 12 (13); breadth of nasals posteriorly 6 (7); interorbital breadth 27 (28); lachrymal breadth 28.4 (31); breadth between tips of postorbital processes 38 (41); zygomatic breadth 41 (44); mastoid breadth 31 (32.6); mandible 40 (41.6); maxillary toothrow (alveoli) 14 (14); mandibular toothrow (alveoli) 14.6 (14.4). _Specimens examined._--One, the type. _Remarks._--While this squirrel exactly resembles the other black backed species with untufted ears, so far as external characters are concerned, it seems to be well differentiated in cranial peculiarities. No black backed _Ratufa_ has hitherto been recorded from the Natunas. RHINOSCIURUS sp. An immature long-nosed squirrel was taken on Sirhassen Island, June 4, 1900. In the absence of material for comparison I am unable to determine the species. The genus is new to the islands. ARCTOGALIDIA INORNATA sp. nov. _Type._--Adult[22] male (skin and skull) No. 104859 U. S. National Museum. Collected on Bunguran Island, North Natunas, June 23, 1900. Original number 502. _Characters._--Much smaller than _Arctogalidia leucotis_ from the Malay Peninsula or _A. stigmatica_ from Borneo (greatest length of skull about 100 instead of 115) and in color paler than either, the dark dorsal stripes obsolete in adult.