OF THE BEAVER AND OP SOME SQUIRRELS. 



1181 



a rod-like ridge to the posterior end of the siipratragus. The 

 tragus is a hard, rounded eminence, and the intertragal notch is 

 very deep. The antitragus is a thick bulging swelling set high 

 above the tragus just beneath the posterior end of the supra- 

 tragus, which fuses with it. The anterior edge rises from the 

 head at a point about on a level with the anterior end of the 

 supratragus and the posterior edge, which is nearh^ straight or 

 slightly sinuous, from a point about on a level with the lower 

 portion of the antitragal prominence. When the ear is closed 

 the upper portion folds down on the supratragus, the antitragus 

 is folded on itself and pulled forwards over the tragus, and with 

 the supratragus blocks the upper part of the cavity, the inter- 

 tragal notch at the same time being closed by the juxtaposition 



Text-fig-ure 44, 



D 



\g^' %^ 



A, B, C. Ear of Euxerus erijtliropus, in three stages of folding. 



D. Ear of Citellus (Otospermophilus) heecheyi, from a dried skin. 



E. ,, ,, Marmota marmota. 



F. „ „ Cynomys ludovicianus. 



of its anterior and posterior walls. Thus the mechanism for 

 closing the ear is quite different from that of the Marmots and 

 Sousliks, where the supratragus is depressed against the hairy 

 thickening invading the fore part of the ear-cavity, the thicken- 

 ing itself being pressed down over the orifice. Judging from a 

 dried skin, the ear of Xerus rutilus is relatively a little smaller 

 than in Utixerus eri/throjncs owing to the reduction in size of the 

 portion above the supratragus. (Text fig, 44, A-C.) 



In Atlantoxerus getulus the ear seems to be relatively a little 

 smaller than in E. erythropus, and projects from the head less 



