Six specimens (one in alcohol) from Bunguran, two from Pulo Lingung, one from Pulo Laut, four (one in alcohol) from Sirhassen, and one (in alcohol) from Pulo Midei. It is doubtful whether these series are referable to one species or whether any of them are the true Bornean _Mus rajah_. The material is not wholly satisfactory, and I have been unable to examine specimens from Borneo. MUS NEGLECTUS Jentink. 1894. _Mus rattus_ var. THOMAS and HARTERT, Novitates Zoologicæ, I, p. 658. September, 1894 (Bunguran). 1895. _Mus neglectus_ THOMAS and HARTERT, Novitates Zoologicæ, II, p. 492. December, 1895 (Bunguran). Five specimens from Pulo Lingung, one from Pulo Midei, and nine from Sirhassen. In the absence of Bornean material, I follow Thomas and Hartert in referring the Natuna rats of the '_alexandrinus_' type to _Mus neglectus_. SCIUROPTERUS EVERETTI Thomas. 1894. _Sciuropterus phayrei_ THOMAS and HARTERT, Novitates Zoologicæ, I, p. 660. September, 1894 (Bunguran). 1895. _Sciuropterus everetti_ THOMAS, Novitates Zoologicæ, II, p. 27. February, 1895 (Revised determination of Bunguran specimens). 1895. _Sciuropterus everetti_ THOMAS and HARTERT, Novitates Zoologicæ, II, p. 490. December, 1895 (Bunguran). Two specimens, both from Bunguran; an immature male taken July 4, and an adult female taken July 21, 1900. PETAURISTA NITIDULA Thomas. 1894. _Pteromys nitidus_ THOMAS and HARTERT, Novitates Zoologicæ, I, p. 660. September, 1894 (Bunguran). 1895. _Pteromys nitidus_ THOMAS and HARTERT, Novitates Zoologicæ, II, p. 490. December, 1895 (Bunguran). 1900. _Petaurista nitidula_ THOMAS, Novitates Zoologicæ, VII, p. 592. December 8, 1900 (Bunguran). Seven specimens from Bunguran. SCIURUS PROCERUS sp. nov. 1894. _Sciurus tenuis_ THOMAS and HARTERT, Novitates Zoologicæ, I, p. 659. September, 1894 (Bunguran). 1895. _Sciurus tenuis_ THOMAS and HARTERT, Novitates Zoologicæ, II, p. 492. December, 1895 (Bunguran). _Type._--Adult male (skin and skull) No. 104698 U. S. National Museum. Collected on Bunguran Island, North Natunas, July 18, 1900. Original number 574. _Characters._--Externally similar to _Sciurus tenuis_ though somewhat smaller. Skull very much smaller and relatively broader than in the related species. _Color._--The color is exactly like that of _Sciurus tenuis_ from Singapore. _Skull and teeth._--Except that it appears to be broader throughout, relatively to its length, the skull of _Sciurus procerus_ is essentially a miniature of that of _S. tenuis_, as the braincase shows none of the tendency to increased depth characteristic of the Bornean animal. Ratio of rostral depth to distance between middle of interparietal and lower rim of audital bulla, 50. This ratio is 49 in _S. tenuis_.