_Characters._--Size slightly less than that of _Sciurus rubidiventris_ and color conspicuously pallid. Upper parts as in _S. lutescens_; lower parts nearly as in _S. seraiæ_ but rather less dull; pale side stripe much less yellow than belly. Skull as in _Sciurus rubidiventris_. _Color._--Upper parts and tail as in _Sciurus lutescens_. Cheeks faintly washed with ochraceous-buff. Under parts and inner surface of legs bright ochraceous-buff (distinctly more yellow than Ridgway's pl. V, No. 10). Lateral stripes as in _S. lutescens_ (not distinctly yellowish as in _S. seraiæ_), but black band usually less sprinkled with gray. Scarcely a trace of gray in axillary region or on sides of neck. _Skull._--The skull in all respects closely resembles that of _S. rubidiventris_ except that it is slightly smaller. Its large size and the correspondingly large teeth readily distinguish it from that of the South Natuna species. _Measurements._--External measurements of type: total length 375; head and body 195; tail vertebræ 180; hind foot 44 (41). Average and extremes of nine specimens from the type locality; total length 363 (355-379); head and body 189 (171-196); tail vertebræ 170 (165-183); hind foot 45 (44-46); hind foot without claws 42 (41-43). _Specimens examined._--Ten (one in alcohol), all from the type locality. _Remarks._--Though suggesting two of the small South Natuna squirrels in color, _Sciurus lautensis_ is obviously related to the dark colored Bunguran form, with which it more nearly agrees in size. SCIURUS NAVIGATOR (Bonhote). 1894. _Sciurus prevostii_ THOMAS and HARTERT, Novitates Zoologicæ, I, p. 656. September, 1894 (Sirhassen). 1901. _Sciurus prevostii navigator_ BONHOTE, Ann. and Mag. Nat. Hist., 7th ser., VII, p. 171. February, 1901 (Sirhassen). Nine specimens, three from Sirhassen Island and six from Pulo Subi. Those from Pulo Subi, while agreeing with the topotypes in color, appear to average a trifle smaller, though the series is hardly extensive enough to prove that this is constant. RATUFA SIRHASSENENSIS (Bonhote). 1894. _Sciurus bicolor albiceps_ THOMAS and HARTERT, Novitates Zoologicæ, I, p. 659. September, 1894 (Sirhassen). 1900. _Ratufa ephippium sirhassenensis_ BONHOTE, Ann. and Mag. Nat. Hist., 7th ser., V, p. 498. June, 1900 (Sirhassen). Two specimens, Sirhassen, June 8, 1900. This species, though related to _Ratufa ephippium_, with which it agrees in color-scheme, is sharply differentiated by its small size and cranial peculiarities. It is in no way closely allied to _Ratufa bunguranensis_ and _R. nanogigas_.