1182 MR. R. I. POCOck ON THE EXTERNAL CHARACTERS 



prominently, but resembles it in other ways sufficiently closely 

 to call for no detailed description. The most important difference 

 is the absence of the tragal thickening in front of the inter- 

 tragal notch, so that the orifice of the ear is exposed. Owing to 

 the reduction in size of the upper free portion, the supratragus 

 is nearer to the summit and the latter is somewhat more 

 pointed. (Text-fig. 43, E.) 



The ear of Geosciurus capensis exhibits the final stage in 

 degeneration in this group * ; but it is clearly derivable from the 

 type seen in Atlantoxerus by the reduction of the upper portion 

 above the supratragus to a rounded thickened rim incapable of 

 being folded downwards and backwards to any appreciable 

 extent on to the supratragus, which is represented at most by a 

 short ridge running forwards and upwards from the antitragus. 

 The latter, as in the other species, is a rounded thickened bulge, 

 less well •defined than in the northern species, set high up and 

 overlapping the posterior portion of the cavity. The anterior 

 rim is overfolded, and its inferior continuation into the cavity is 

 represented at most by a small excrescence opposite the anti- 

 tragus. There is no tragus, as in Atlantoxerus, the orifice being 

 exposed at the bottom of the deep intertragal notch. The ear 

 is closed by the forward movement of the thicker posterior border 

 of the cavity against the anterior, there being no folding of the 

 antitragus or upper rim. (Text-fig. 43, F.) 



The structure of the ears in these Bristly Ground Squirrels is 

 not opposed to the view of their affinity with the African species 

 referred to Funiscmrus, but the difl:erences supply no evidence 

 of close affinity. 



In fktstor the ear is relatively small, but is as free from the 

 integument of the head as in the typical Sciuridfe. Its outer 

 surface is flat, and the anterior edge is not overfolded ; it is 

 uniformly covered with hair except i^ound the cavity, whei-e it is 

 naked. The cavity is a small, irregularly triangular space bounded 

 above by the supratragus, which is overlapped in front by the 

 anterior Q6.gQ which runs downwards and backwards to the 

 orifice lying at the bottom of the cavity and concealed by the 

 lower edge of the cavity corresponding to the intertragal notch. 

 The posterior border of the cavity forms a convex bulge probably 

 representing the antitragus, but there is no trace of tragus. 

 (Text-fig. 40, C.) 



The characters of the principal types of ears above described 

 may be summarised a,s follows : — ■ 



a. Ear simple, its anterior edge above the supratragus not over- 

 folded Castor. 



a'. Ear simple or complex, its anterior edge above the supratragus 

 overfolded. 

 b. Cavity of the ear, when folded, mainly closed by hairy, 

 thickened continuation of the overturned anterior rim beneath 

 the supratragus, np tragus or antitragus ... CiieUus, Cynormis, Marmota. 



* Described by W. L. Sclater as follows : — Ear conch completely absent, the ear- 

 opening being a narrow diagonal slit half an inch in length. 



