40.7 (39-42).

Cranial measurements of type: greatest length 45.4 (50.4)[19]; basal length 39 (43); basilar length 36.4 (41); palatal length 20 (23); palatal width between middle molars 6 (6); greatest length of nasals 13 (14.8); greatest width of both nasals together 6.6 (7); interorbital breadth 15.4 (17); mastoid breadth 21 (21); zygomatic breadth 26 (29); depth of braincase at anterior edge of basi-occipital 16 (16.8); mandible 28 (30); maxillary toothrow (alveoli) 8 (9); mandibular toothrow (alveoli) 8 (9).

Specimens examined.—Seven (one in alcohol), all from the type locality.

Remarks.—This squirrel is recognizable among the members of the S. notatus group by its light colors, and particularly by the pallor of the under parts. In the latter characteristic it is approached by the form inhabiting Pulo Laut, but with this exception it is unique among the fulvous bellied species. The six specimens show no variation worthy of note.

SCIURUS SERAIÆ sp. nov.

Type.—Adult male (skin and skull) No. 104660 U. S. National Museum. Collected on Pulo Seraia, South Natuna Islands, May 29, 1900. Original number 415.

Characters.—Most nearly related to the small, pallid, Sciurus lutescens from Sirhassen Island, but upper parts slightly less pale, and under parts and pale side stripe buff-yellow, the former without admixture of gray.

Color.—Upper parts as in Sciurus lutescens except that the pale bands on the hairs are more nearly buff than cream-buff. Tail essentially as in S. lutescens but a shade less pale. Under parts buff-yellow darkening irregularly to dull orange-buff. Dark side stripe broad and well defined.

Skull.—The skull closely agrees with that of Sciurus lutescens in both size and form, though it is perhaps even broader in proportion to its length. Teeth as in S. lutescens.

Measurements.—External measurements of type: total length 368; head and body 197; tail vertebræ 171; hind foot 44 (40). Average and extremes of four specimens from the type locality: total length 347 (323-368); head and body 184 (171-197); tail vertebræ 163 (152-171); hind foot 43.7 (43-45); hind foot without claws 40.1 (39.5-41).

Cranial measurements of type: greatest length 45; basal length 38.6; basilar length 36; zygomatic breadth 26.4; least interorbital breadth 17; mandible 28; maxillary toothrow (alveoli) 8.6; mandibular toothrow (alveoli) 8.6.

Specimens examined.—Four, all from the type locality.

Remarks.—As might be expected from the geographic position of the island it inhabits, Sciurus seraiæ differs from the Bornean S. notatus in much the same way as the Sirhassen representative of the group. It is readily distinguishable from the Sirhassen animal by the different color of the under parts. In color Sciurus seraiæ closely resembles S. abbottii of the Tambelan Islands. The latter is, however, a much larger animal, with a longer and relatively narrower skull.

SCIURUS RUTILIVENTRIS sp. nov.

Type.—Adult male (skin and skull) No. 104658 U. S. National Museum. Collected on Pulo Midei (Low Island), South Natuna Islands, May 24, 1900. Original number 405.

Characters.—Size slightly greater than that of Sciurus lutescens and S. seraiæ, but not equal to that of the Bornean or Bunguran representatives of S. notatus. Color above as in S. seraiæ. Under parts bright clear orange-rufous.

Color.—Color exactly as in Sciurus seraiæ except that the pale side stripe is light cream-buff and the under parts are bright orange rufous. Tail without trace of red suffusion.

Skull and teeth.—The skull and teeth are a trifle larger than in Sciurus lutescens and S. seraiæ, but the difference is scarcely a tangible one.

Measurements.—External measurements of type: Total length 368; head and body 190; tail vertebræ 178; hind foot 45 (41). Average and extremes of seven specimens from the type locality: total length 356 (330-368); head and body 186 (178-190); tail vertebræ 173 (165-184); hind foot 45.5 (43-48); hind foot without claws 42.2 (39.5-45).

Specimens examined.—Seven, all from the type locality.

Remarks.—This squirrel is remarkable among the Natuna members of the S. notatus group for the brilliant color of its under parts. In this respect it surpasses all of the related forms with which I am acquainted. The red color is, however, strictly confined to the body, showing no tendency to spread to the tail as in S. miniatus of the Malay Peninsula.

SCIURUS RUBIDIVENTRIS sp. nov.

1894. Sciurus notatus Thomas and Hartert, Novitates Zoologicæ, I, p. 659. September, 1894 (part, specimens from Bunguran).

1895. Sciurus notatus Thomas and Hartert, Novitates Zoologicæ, II, p. 491. December, 1895 (part, specimens from Bunguran).

Type.—Adult female (skin and skull) No. 104671 U. S. National Museum. Collected on Bunguran Island, North Natunas, June 22, 1900. Original number 498.

Characters.—Size and general appearance both above and below as in the Bornean form of Sciurus notatus, but red of under parts brighter, and cheeks and chin distinctly less fulvous than surrounding parts. Skull with broader, deeper braincase than in the Bornean animal.

Color.—The color so closely resembles that of the Bornean Sciurus notatus that no detailed description is necessary. Under parts ochraceous-rufous, fading to tawny on throat, everywhere lighter and more tinged with red than in the Bornean animal. In the latter the color of the under parts extends forward to lips and also strongly suffuses the cheeks and sides of head which are only a shade browner than the throat and conspicuously more fulvous than top of head and sides of neck. In Sciurus rubidiventris the cheeks and lips are noticeably suffused with gray so that they form a distinct contrast with both throat, top of head and sides of neck.

Skull.—The skull agrees in general size with that of the Bornean animal, and is therefore much larger than in the three species from the South Natunas. It is distinguishable by greater general breadth and by the depth of the braincase, which perceptibly exceeds that of S. notatus.

Measurements.—External measurements of type: total length 380; head and body 209; tail vertebræ 171; hind foot 49 (44.5). Averages and extremes of seven specimens from the type locality: total length 378 (368-393); head and body 208 (203-222); tail vertebræ 173 (165-184); hind foot 49.3 (48-50); hind foot without claws 45.7 (44.5-47).

Cranial measurements of type: greatest length 52.4 (50.4);[20] basal length 44 (43); basilar length 41 (41); palatal length 23 (23); palatal width between middle molars 6 (6); greatest length of nasals 15 (14.8); greatest width of both nasals together 7.2 (7); interorbital breadth 18.2 (17); mastoid breadth 23 (21); breadth of braincase above roots of zygomata 24 (22); zygomatic breadth 30.4 (29); depth of