SCIURUS 685 



surprising variations of form within the limits of the old genus 

 Sciurus ; and the modern classification of this unwieldy group, 

 now developing, will no doubt largely rest upon the characters 

 afforded by this organ {Ann. Mag. Nat. Hist., April 191 5, 



383). 



The family dates from the Upper Oligocene, at least, in 

 Europe and North America. Apart from some Sciurid remains 

 from the Oligocene of Wight, which appear to represent a 

 forerunner of Sciuropterus rather than a member of the present 

 family, its British representatives belong to two genera, Sciurus 

 and Citellus ; both of them are members of the sub-family 

 Sciurincs. Citellus is only known from our Pleistocene 

 deposits ; but Sciurus has still a representative living in these 

 islands. 



Genus SCIURUS. 



1758. Sciurus, C. Linnaeus, Syst. Nat., loth ed., i., 63 ; genotype -vulgaris, selected 

 by tautonymy. 



1893. Aphrontis, Schulze, Zeitsch.f. Natttrwissensch., Leipzig, Ixvi., 165 ; based on 

 Sciurus vulgaris. 



Squirrels of arboreal habits, whose general external appear- 

 ance, cranial, dental, and other internal characters are closely 

 similar to those of the well-known European and British 

 species, are widely distributed throughout the wooded parts of 

 Eurasia and the New World. They represent a very large 

 number of species ; and until quite recently all have been 

 referred to the genus Sciurus. The latter indeed had swollen 

 to such embarrassing dimensions that Miller found it "impos- 

 sible to frame a satisfactory diagnosis of the genus Sciurus, or 

 to estimate the number of forms that should be referred to the 

 group." 



Thomas {op. cit., p. 384) describes the baculum of 

 5. vulgaris (including S. leucourus) as being a " very character- 

 istic bone, like a small spatula, or still more like a half-closed 

 human right hand, the shaft forming the fore-arm, the blade of 

 the spatula the hollowed palm, and a small pointed projection 

 on the right side corresponding to an outstretched thumb." 

 Bacula of this type are found also in the two other Palaearctic 

 species — S. persicus and S. lis ; in all the American species — 

 VOL. iL 2x2 



