686 SCIURIDA&—SCIURUS 
so far as Thomas has been able to examine them in this 
respect; and ‘remarkable to say” in the Giant Squirrel 
(Retthrosciurus) of Borneo. In all the Indian and Malayan 
species the baculum is more complex, being provided with a 
more or less well-developed, separate cutting-blade, articulated 
with and attached to the shaft of the bone by ligaments ; 
Thomas has therefore removed all these arboreal squirrels from 
the genus Sczwrus, reviving Gray’s Ca//oscturus for one section, 
and instituting his own genus 7omewtes for another. 
A few weeks after the publication of Thomas’s paper, Allen 
(Bull. Amer. Mus. Nat. Hist., xxxiv., May 1915, p. 171), 
reviewing the South American Sczuvzd@, removed ‘“‘the genus 
Sciurus from the American biota” and referred all American 
squirrels to other generic divisions. Whether such a drastic 
course is quite justified may be open to some question; but as 
to its convenience there can be none. 
The genus Sczwvus, as understood at present, therefore 
comprises merely four living species, viz., S. vadgaris, ranging 
through the whole of Europe and a large part of northern and 
central Asia; S. Zeucourus, inhabiting Britain and Ireland; 
S. persicus, from Asia Minor and Persia; and Sy 1/25, Bi 
inhabitant of Japan. In addition several European fossil 
species, dating from the Eocene onwards, are at present referred 
to “ Sczurvus” ; but in their case the generic name is merely a 
confession of ignorance ; for the fossils hitherto found, although 
ample to demonstrate the former existence of species with jaws 
and teeth more or less similar to those of living Sczzzus, are 
wholly insufficient as a basis for determining the fine generic 
distinctions of modern mammalogy. 
The leading characters of the genus Sczwrus, as defined 
above, may be summarised as follows :—Squirrels of essentially 
arboreal habits, medium size, and typical outward appearance ; 
with a bushy, vertically compressed tail, whose length exceeds 
half the length of the head and body. The baculum is simple, 
as above described. The skull is deep, with a well-arched and 
relatively capacious brain-case, and a short rostrum ; the supra- 
orbital outgrowths are large and terminate behind in slender 
postorbital processes. In the dentition the incisors are 
strongly compressed, much deeper than broad in transverse 
