897 



Family SCIURID^. 

 1821. Sciuridm Gray, London Med. Eepos., xv, p. 304, April 1, 1821. 



Geographical distribution. — Eastern and western hemispheres 

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

 New Guinea, Australia and the Pacific Islands. 



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

 .habits are 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 ; infraorbital foramen 

 small ; jugal long, its anterior extremity wedged between 

 lachrymal and zygomatic process of maxillary ; palate rather 

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

 lower incisor with root not extending conspicuously into 

 ascending portion of ramus ; molars rooted, tubercular and 

 transversely ridged, premolars -f or -}. 



Remarks. — The family Sciuridte, 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 EUBOPEAN GENERA OF SCIXJBID^E. 



(For convenience of comparison the cranial and dental characters of 

 Scitiroptcrus are 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 Sciuropterus, p. 941.] 



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 parallel. 

 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) _• Soiurus, 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). 



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