CITELLUS 927 



in S. vnlgari.% and exposed portion of petrosal noticeably smaller ; 

 paroccipital processes rather large, their extremities reaching 

 beyond level of lower edge of condyle and often to that of 

 lower edge of bulla ; basioccipital essentially like that of Sciuriis 

 vulgaris in general form, but anterior portion of outer margin 

 raised into a conspicuous plate-like process applied to inner side 

 of bulla ; auditoi-y bulla essentially as in Sciurns vidgaris but more 

 evenly though somewhat less inflated. Interorbital region much 

 longer than broad, its least width less than that of postorbital 

 constriction, its surface nearly flat except for the curve of which 

 it forms a part ; edges of orbits slightly raised above the general 

 level, the supi'aorbital notch inconspicuous ; postorbital processes 

 relatively shorter than in Sciurus vulgaris, the space lying 

 between process and surface of brain-case narrower ; orbit 

 surrounded by bone through about two-thirds of its circum- 

 ference. Zygomata diverging gradually and evenly, nowhere 

 parallel, the greatest zygomatic breadth at or just in front of 

 glenoid level ; jugal projecting posteriorly as in Sciurus vulgaris 

 though less noticeably, its upper border without angle at 

 posterior limit of orbit ; anterior zygomatic root with conspicuous 

 projecting ridge extending along its entire anterior border ; 

 anteorbital foramen sub-circular in outlme, its position somewhat 

 more anterior in relation to tooth-row than in Sciurus vulgaris, 

 its entire lower and outer border thickened and lip-like. 

 Rostrum forming about one-third length of skull, its base not 

 noticeably broader than anterior region, the least depth behind 

 incisors about equal to width at same level ; nasals relatively 

 longer than in Sciurus vulgaris, extending about to lachrymal 

 level, the posterior border variable, usually truncate ; nasal 

 branches of premaxillaries broad but not expanded, rarely 

 extending behind nasals. Palate less concave both longitudinally 

 and laterally than in Sciurus vulgaris ; a low but evident median 

 ridge extending from incisive foramina to spine or blunt pro- 

 jection at posterior border ; incisive foramina about as large as 

 in S. vulgaris, but more distinct from each other, and .anterior 

 extremity not gradually narrowed to a fine point ; mesopteiygoid 

 fossa about three times as long as wide, narrowest near middle ; 

 ectopterygoid rather well developed, forming a wide flattened 

 area nearly as large as mesopterygoid space. Mandil^le less 

 robust than that of Sciurus vulgaris, the ramus in region near 

 symphysis scarcely deeper than wide ; coronoid process longer 

 and more curved than in S. vulgaris, its anterior border much 

 more convex ; articular process slender, deeply concave on outer 

 side ; angular process with anterior limit less well defined. 



Teeth. — Upper incisor less robust than that of Sciurus 

 vulgaris, but course of shaft very distinctly marked on side of 

 rostrum from alveolus to anteorbital foramen ; cross section of 

 shaft nearly semicircular in outline, the flattened side turned 

 inward ; enamel extending from antcu'O-internal extremity nearly 



