OF THE BEAVEE AND OF SOME SQUIRRELS. 1177 



absence of the genal tufts the Castoridse differ from the Sciuridae 

 and Petauristidas. 



The systematic results yielded by the characters discussed njay 

 be tabulated as follows : — 



a. Rliinarium unhooded, not wliollj^ naked, nostrils wido apart, 

 lateral, valvular; upper lip uncleft; mouth with a bristly 



pad inside the cheek ; no genal vibrissa Castorida. 



a'. Khinarium hooded, i. e. capable of being- covered by a flap of 

 skin from the upper surface of the nose, naked, nostrils close 

 together, looking forwards, not valvular ; upper lip deeply 

 cleft to rhinarium ; mouth without bristly pad inside cheek"; 



genal vibrissas present Sciuridce & Pefauristidcs. 



h. Two tufts of superciliary vibrissge, an anterior and a posterior. 



Xerus and its allies. 

 h'. OyAj the normal anterior tuft of vibrissge present. 



c. Interramal tuft of vibrissse present Sciurida (including Xertis). 



c' Interramal tuft of vibrissa absent Fetauristidce. 



The Ear. 



In the arboreal Squirrels the ear exhibits no marked struc- 

 tural variations. That of Scmrus vulgaris may be described as 

 typical. It is oval in shape and stands away from the head from 

 a point in front about on a level with the supratragus, and behind 

 from a point below the antitragus. The anterior edge is folded 

 over from the summit or tip of the ear, and the overfolded rim 

 increases in thickness down to the supratragus. Beneath the 

 supratragus the edge runs obliquely downwards and backwards 

 into the cavity of the ear, and ceases on its inner wall about 

 midway between the supratragus and the orifice of the ear. The 

 orifice lies at the bottom of the cavity just below the level of the 

 intertragal notch, which is defined in front by a small hemi- 

 spherical tragus and behind by a large angular antitragns. The 

 latter fits over the tragus when the ear is closed, and posteiiorly 

 is continuous with a large flap resulting from the overfolding of 

 the posterior rim from a point a little above the line of the 

 supratragus. The supratragus is a ridge with sharply defined 

 inferior and poorly defined superior eAga. It forms the upper 

 border of the cavity of the ear, separating it from the feebly 

 hollowed upper portion, which in height exceeds the height of 

 the cavity. (Text-fig. 42, A.) 



Judging from dried skins and material preserved in spirit, the 

 ears of the American species S. hudsonicus, carolmensis, niger 

 [rufiventer), griseus, saUtcensis, hypopyrrhus and of several fornas 

 I'elated to the last, resemble in all essentials those of S. vulgaris. 

 So also do the ears of Uuiamias, and of the Petauristidae of the 

 genera Glaucomys. Eoglaucomys and Petaurista, with the excep- 

 tion that in those Flying Squirrels the pinna is still more 

 extended above the supratragus and the anterior edge is not 

 overfolded to the summit. (Text-fig. 42, B, E, F.) 



The ears of the Tropical Asiatic and African arboreal Squirrels 

 differ from those of Sciurus vulgaris and of the American species 

 above referred to in being shorter as compared with their antero- 

 posterior width, in being less tubular at the base, so that the 



