consists of two transverse folds, and an anterior internal tubercle. There is no trace of the supplementary outer tubercles of the corresponding tooth of Mus validus.

Measurements.—External measurements of type: total length 463; head and body 235[13] tail vertebræ 228;[13] hind foot 48 (45); ear from meatus 19; ear from crown 15; width of ear 15. In adult male topotype: total length 462; head and body 234;[13] tail vertebræ 228;[13] hind foot 46 (44); ear from meatus 21; ear from crown 16; width of ear 16.

Cranial measurements of type: greatest length 52 (55);[14] basal length 45 (48.6); basilar length 41.6 (45.6); palatal length 23 (26); least width of palate between anterior molars 5 (5); diastema 14 (14.6);[15] length of incisive foramen 8 (9); combined breadth of incisive foramina 3 (3.6); length of nasals 21 (22.6); combined breadth of nasals 6 (6.2); zygomatic breadth 25 (28); interorbital breadth 8 (8); mastoid breadth 19 (19); breadth of braincase above roots of zygomata 18.8 (20); depth of braincase at anterior border of basi-occipital 12.8 (15); frontopalatal depth at posterior extremity of nasals 12.8 (13.4); least depth of rostrum immediately behind incisors 10 (10); maxillary toothrow (alveoli) 9.6 (11); width of front upper molar 3 (3); mandible 30 (31); mandibular toothrow (alveoli) 9 (10).

Specimens examined.—Four, three from the type locality, and one from Pulo Lingung.

Remarks.—This rat is probably a near relative of the Bornean Mus mülleri of Thomas.[16] The specimen from Pulo Lingung does not differ appreciably from the others.

MUS SABANUS Thomas.

1887. Mus sabanus Thomas, Ann. and Mag. Nat. Hist., 5th ser., XX, p. 270. October, 1887 (Mt. Kina Balu, Borneo).

1894. Mus sabanus Thomas and Hartert, Novitates Zoologicæ, I, p. 658. September, 1894 (Bunguran).

Thirteen skins and one extra skull, all from Bunguran. There is little probability that this rat is the same as the true Mus sabanus of Borneo.

MUS RAJAH Thomas.

1894. Mus hellwaldi Thomas and Hartert, Novitates Zoologicæ, I, p. 658. September, 1894 (Bunguran).

1894. Mus rajah Thomas, Ann. and Mag. Nat. Hist., 6th ser., XIV, p. 451. December, 1894 (Mount Batu Song, Borneo).

1895. Mus rajah Thomas, Novitates Zoologicæ, II, p. 26. February, 1895 (Revised determination of Bunguran specimens).

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