SCIURUS 685 
surprising variations of form within the limits of the old genus 
Scturus ; 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 1915, 
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 Sczuropterus rather than a member of the present 
family, its British representatives belong to two genera, Sczurus 
and Cztellus; both of them are members of the sub-family 
Sciurine. Citellus is only known from our Pleistocene 
deposits ; but Sczwrus has still a representative living in these 
islands. 
GENUS SCIURUS. 
1758. SCIURUS, C. Linnzeus, Syst Mat., 1oth ed., i. 63; genotype vulgaris, selected 
by tautonymy. 
1893. APHRONTIS, Schulze, Zectsch. f. Naturwissensch., 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 Sczwrus. The latter indeed had swollen 
to such embarrassing dimensions that Miller found it ‘impos- 
sible to frame a satisfactory diagnosis of the genus Sczurus, or 
to estimate the number of forms that should be referred to the 
group.” 
Thomas (of. czt., p. 384) describes the baculum of 
S. vulgaris (including S. deucourus) 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 Palzarctic 
species—S. persicus and S. Zs; in all the American species— 
VOL. II. 2X2 
