1915.| Allen, Review of the South American Sciuride. 299 
exception of the genus Sciurillus, to be further noticed later) to the Carib- 
bean border and the Andean region. They include the genera Microsciurus, 
Mesosciurus, Notosciurus, and Leptosciurus. The squirrels with 8 mamme 
-occupy exclusively all the rest of the squirrel-inhabited parts of the conti- 
nent, from’ the eastern slope of the Andes to the Atlantic coast. They 
include the genera Guerlinguetus, Hadrosciurus, Uroscwurus, and Simoscwurus, 
in other words, the guerlinguets and the ‘giant’ squirrels. Szmosciurus, a 
member of the latter, however, presents a partial exception, having pene- 
trated to the Pacific slope along the Ecuador-Peru boundary. 
All South American squirrels have the premolar formula 7, except the 
genera Microsciurus and Sciurillus, which have the premolar formula 2. 
ies 
ee f. | 
x 
oye C25 
i> a Pah 
tx g SPA 
PSs fea pi iat 
= ee. *e 
SS rp ORY 
Fig. 23. Mesosciurus. 1, Subgenus Mesosciurus: 2, subgenus Histriosciurus. 
Microsciurus ranges from Costa Rica to southern Peru, but is confined in 
South America to the Andean or Cordillera region, and in Colombia to the 
western part of this area, it not extending to the Eastern Andes, and being 
absent from the Bogoté region and the Merida and Maritime ranges of 
Venezuela. Its altitudinal range in western Colombia is from sea level to 
paramo. Sciurillus, on the other hand, is known only from the Guianas, 
and from only a few specimens, and is hence unrepresented in nearly all 
museums. Itisa very ancient type, has no close relationship with any other 
American genus, and is among the smallest of known squirrels. Its affini- 
ties are with the Nannosciurine, to which it has been referred by Thomas 
