897 



Family SCIUUID^. 



18:21. Sciurichc. Gray, London Med. Kopos., xv, p. 301, April 1, 1821. 



Geograpldcal distrihution. — Eastern uTid western hemispheres 

 except at the extreme north and south ; absent from Madagascar, 

 New Guinea, Austraha and the Pacific Islands. 



Chantctcrs. — Form slender or robust according as the animal's 

 habits ai'e arboreal or terrestrial ; tail without horny scales on 

 lower surface, densely long-haired, usually flattened ; ribs twelve 

 or thirteen pairs ; skull varying in form but never highly 

 modified ; postorbital processes present ; infi'aorbital foi'ameu 

 small ; jugal long, its anterior extremity wedged between 

 lachrymal and zygomatic pi'ocess of maxillary ; palate rather 

 broad ; upper incisor with root in front of anterior cheek-teeth, 

 lower incisor with root -not extending conspicuously into 

 ascending jwrtion of ramus ; molars rooted, tubercular and 

 transversely ridged, premolars j or }-. 



HevtarJcs. — The family Scmridse, containing the squirrels, 

 spermophiles, marmots and their allies, is one of the most widely 

 distributed and abundantly represented group of rodents. It 

 contains about forty-five living groups, the exact status of many 

 of which is still in doubt ; three of these occur in Europe. 



KEY TO THE EUROPEAN GENERA OP SCIURID^^. 



(For convenience of comparison the cranial and dental cbaracters of 

 Sciuroptcrus arc inserted.) 



[Orbit large, its vertical diameter equal to more 

 than one-third basilar length of skull ; posterior 

 transverse ridge on crown of first and second 

 upper molar terminating internally in a distinct 

 cusp isolated by deep groove ; axes of enamel 



foldings of lower cheek-teeth not parallel Scluropterns, p. 911.] 



Orbit moderate or small, its vertical diameter equal 

 to less than one-third basilar length of skull ; 

 posterior transverse ridge on crown of first and 

 second upper molar terminating internally with- 

 out cusp and groove ; axes of enamel foldings of 

 lower cheek-teeth isarallel. 

 Incisors compressed, the width of anterior face not 



more than half that of lateral face ; small 



upper premolar minute, its crown simple, with 



diameter equal to about one-eighth that of 



large premolar ; dorsal profile of skull strongly 



depressed posteriorly ; tail nearly as long as 



head and body, very bushy (Habits arboreal. 



Squirrels) Sciurus, p. 898. 



Incisors not compressed, the width of anterior face 



about equal to that of lateral face ; small 



upper premolar well developed, its crown 



marked by evident ridges and depressions, its 



diameter about half that of large premolar ; 



dorsal profile of skull not very strongly de- 

 pressed posteriorly (Habits terrestrial). 



3 Ji 



