- Famity SCIURID A. 
The family Sciuride, as now commonly restricted, may be characterized 
as follows: Dental formula; I. +; Pm. = or #2; M. $3 =15 or 30. 
Grinding-teeth rooted, with, during youth, tuberculated crowns ; the tubercles 
soon becoming much modified or obliterated by attrition, generally giving 
rise for a time to transverse ridges. he first upper premolar, when two are 
present, is often minute, and is generally much smaller than the second. In 
strictly congeneric species, in Sciurus and Tamias, the premolars may be 
either two or one. Occasionally two are present in species that have usually 
only one. In species having a single premolar, a second deciduous premolar 
is generally assumed to have been present during early life, but to this there 
are frequent exceptions. The first upper premolar, when two are present, 
is always single-rooted, with a simple pointed crown, and is often so minute as 
to be apparently functionless. The other upper grinding-teeth are triple- 
rooted. The lower premolar is double-rooted, the last lower molar generally 
triple-rooted, and the others quadruple-rooted. 
The skull varies considerably in form, from the short, broad skull of the 
arboreal Squirrels to the narrow, very much elongated skull of some of the 
Spermophiles. There isa well developed postorbital process, which may be 
either short, pointed, and triangular, or long, slender, and much decurved. 
oS. 
The infraorbital foramen is small, and placed considerably in advance of the 
zygomatic process of the maxillary (usually about midway between the ante- 
rior premolar and the maxillo-intermaxillary suture), and varies from a nar- 
row vertical slit to an oval or triangular opening. The palate is very broad 
and flat, and extends posteriorly considerably beyond the last molar (except 
in some exotic species), and forms a continuous uniform plane. Molar series 
parallel. Feet scansorial or fossorial. Tail long or short, terete and slender 
or bushy and distichous, always well haired. Body generally elongate, 
637 
