SCIUROPTERUS 



943 



less of the surface of parietal is visible ; occiput very low, its 

 height above lower lip of foramen magnum about one-half 

 mastoid breadth, its dorsal and lateral margins forming a flattened 

 curve much less than a semicircle in extent ; foramen magnum 

 decidedly wider than high ; surface of occipital with very obscure 

 swellings between foramen magnum and lambdoid ridge ; par- 

 occipital processes very slender ; basioccipital rather narrow and 

 long, its width anteriorly about one-half median length, its 

 lateral ridges obsolete, not tending to form processes as in Sciurus 

 vulgaris and Citellus ; auditory bullae sub-circular in general 

 outline, their form essentially as in Sciurus vulgaris, but their 



Fig. 19;'). 

 Sciuropterus russicun. Nat. size. 



size actually as well as relatively greater, the antero-posterior 

 diameter equal to distance from front of bulla to front of j^i, the 

 lateral diameter to outer margin of meatus fully 1^ times least 

 width of basioccipital ; anterior upper margin of meatus developed 

 into a conspicuous forward-curved flange ; jjetrosal tending to be 

 exposed in region above meatus instead of on occipital surface. 

 Interorbital region decidedly longer than broad, its surface 

 noticeably concave laterally, so that bases of ])ostorbital processes 

 are evidently above level of median region ; notch at anterior 

 base of postorbital process large, always open ; postorbital 

 processes long and slender, strongly curved downward, the orbit 



