686 SCIURID^—SCIURUS 



so far as Thomas has been able to examine them in this 

 respect ; and " remarkable to say " in the Giant Squirrel 

 {Reithrosciurus) 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 Sciurus, reviving Gray's Callosciurus for one section, 

 and instituting his own genus Tomeutes 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 SciuridcB, removed " the genus 

 Sciurtis 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 Sciurus, as understood at present, therefore 

 comprises merely four living species, viz., S. vulgaris, ranging 

 through the whole of Europe and a large part of northern and 

 central Asia ; 5". leucourus, inhabiting Britain and Ireland ; 

 S. persicus, from Asia Minor and Persia ; and 5". lis, an 

 inhabitant of Japan. In addition several European fossil 

 species, dating from the Eocene onwards, are at present referred 

 to ''Sciurus" ; 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 Sciurus, are 

 wholly insufficient as a basis for determining the fine generic 

 distinctions of modern mammalogy. 



The leading characters of the genus Sciurus, 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 



