_Measurements._--External measurements of type: total length 235; head and body 140; tail vertebræ 95; hind foot 35 (33). Average and extremes of four specimens from the type locality: total length 239.5 (235-247); head and body 140; tail vertebræ 99.5 (95-107); hind foot 35.2 (34-36.5); hind foot without claws 32.9 (31.8-34). Cranial measurements of type: greatest length 34 (38);[17] basal length 28.6 (32); basilar length 26 (29); palatal length 14.6 (16); diastema, 7.6 (8.8); length of nasals 10.4 (11.4); greatest breadth of nasals 4.8 (5.6); interorbital breadth 12 (12.6); zygomatic breadth 20.8 (21); greatest breadth of braincase 17 (17.6); cranial depth from middle of interparietal to lower rim of audital bulla 14 (15); least depth of rostrum 7 (7.2); mandible, 20 (21); maxillary toothrow (alveoli) 6 (7); mandibular toothrow (alveoli), 6 (7). _Specimens examined._--Six, all from the type locality. _Remarks._--This species is immediately distinguishable from its allies by its small skull, scarcely larger than that of _Funambulus macclellandi_. SCIURUS NATUNENSIS (Thomas). 1894. _Sciurus lowi_ THOMAS and HARTERT, Novitates Zoologicæ, I, p. 659. September, 1894 (Sirhassen). 1895. _Sciurus lowi natunensis_ THOMAS, Novitates Zoologicæ, II, p. 26. February, 1895 (Revised determination of Sirhassen specimen). 1895. _? Sciurus lowi natunensis_ THOMAS and HARTERT, Novitates Zoologicæ, II, p. 491. (Bunguran and Pulo Laut.) Four specimens from Sirhassen. The average and extreme measurements are as follows: total length 222 (215-229); head and body 135 (133-140); tail vertebræ 86 (82-89); hind foot 33.6 (33-35); hind foot without claw 31.5 (30.5-32). SCIURUS LINGUNGENSIS sp. nov. 1895. _? Sciurus lowi natunensis_ THOMAS and HARTERT, Novitates Zoologicæ, II, p. 491. (Bunguran and Pulo Laut.) _Type._--Adult male (skin and skull) No. 104693 U. S. National Museum. Collected on Pulo Lingung off southern extremity of Bunguran, North Natuna Islands, June 19, 1900. Original number 494. _Characters._--Externally similar to _Sciurus natunensis_ (Thomas), but slightly larger (hind foot with claws 36 instead of 33.6). Skull larger than that of _S. natunensis_, the audital bullæ much broader anteriorly. _Color._--The color is precisely as in _Sciurus natunensis_, and therefore requires no detailed description. _Skull._--Skull larger than that of _Sciurus natunensis_ (see measurements) but not different in general form. The audital bullæ are, however, readily distinguishable by the much greater development of the anterior inner lobe. In _Sciurus natunensis_ this lobe is so small as scarcely to form any part of the general contour of the bulla. In _S. lingungensis_ it is nearly equal to the anterior outer lobe, together with which it imparts a distinctly triangular outline to the ventral aspect of the bulla.