1915.] Allen, Review of the South American Sianiae: 187 
SoutH AMERICAN SCIURIDZ. 
In the following pages the tree squirrels of South America are divided 
into nine natural and, for the most part, geographically and morphologically 
well-circumscribed groups. They are here treated, partly for nomenclatural 
convenience, as full genera. Their ultimate valuation will naturally vary 
with the viewpoint of the taxonomer. The reasons for this proposed sub- 
division have already been stated (pp. 169-172). Illustrations of the cranial 
characters are given of the leading types in Plates VII-XIV.! 
_ The forms here recognized (including 5 from Central America) number 
76, of which 38 are given the status of species, with 38 additional subspecies. 
The ‘giant’ squirrels of the Amazonian region are unfortunately poorly 
represented in the material available for study, and the recognition 
accorded to several of the forms of this group is merely provisional. 
Five genera (Leptosciurus, Mesosciurus, Hadrosciurus, Urosciurus, 
Simosciurus), one subgenus (Histriosciurus), and two subspecies (Guerlin- 
guetus estuans venustus, Mesosciurus gerrardi baudensis and M. g. valdivie) 
are here characterized as new. [For the last two see Addenda, p. 308.| 
Key to the Genera? 
Mamme, 6. 
Premolars, %. 
Size small, total length about 240-260 mm., hind foot 35-40; tail much 
enorcer than head and body eo)... iu. A ees Microsciurus (p. 188) 
Size very small, total length about 220 mm., hind foot about 28; tail as 
long as or longer than the’ body. 2... 3.36.4. ee Sciurillus (p. 196) 
Premolars, +. 
Size small, total length about 320-380, hind foot 40-45; tail shorter than 
head and body. 
Soles naked, plantar pads normal....... i Leptosciurus (p. 199) 
Soles heavily furred nearly the whole length, plantar pads all near 
ea AI a ne ov ae Pais woe Notosciurus (p. 209) 
Size medium, total length about 375-450 mm., hind foot 50 to 55; tail 
about equal to or shorter than head and body....Mesosciurus (p. 212) 
Mamme, 8; premolars, +; tail as long as or longer than head and body. 
Wega TA ATPON i a Oh oe ae eS Guerlinguetus (p. 254) 
Size large, total length 490-580, tail broad and bushy. 
Skull broad and heavy, rostrum short...... Hadrosciurus (p. 265) 
Skull long and narrow, rostrum slender........ Urosciurus (p. 267) 
Size large, tail very long and narrow, skull short, rostrum very short and 
ME 9 as ey ah es HOES Sie sted Re aires eee 2 Simosciurus (p. 280) 
1 For explanation of the Plates (Pll. VII-XIV) see pp. 286-288. 
2 For maps showing the distribution of the genera see pp. 298-301. For a sketch-map 
showing localities in southwestern Colombia from which squirrels have been examined in 
the preparation of this review, see this Bulletin, Vol. XXXIII, 1914, pl. xiii. 
