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MONOGUAPDS OF NOUTU AMEUICAN RODENTIA. 



Tadlk V. — Lilt of ipccimcKt aamimd of SciunurTEiti's volccella Mr. volucella — CoDliniicd. 



Gekus SCIURUS Linnaeus. 



jSciHrua LiNNiGL-8, Syst. Nat. 10th ed. 1758 (in part), and of most sabseqiieot aothon. 



itaaroxut F. CoviKR, " Diet, dea Sci. Nat. x, 181B" ' ; il6m. da Mas. x, ie2.'i, ItS ; Deuts des Mam. 1825, 



161 ; Diet, des Sci. Nat. lix, 1839, 474. (Type &ji«r«< a$tiiant Linn.) 

 UaeroxHt Okay, Add. & Mag. Nat. Hist. 3d 8er. zx, lUu7, 275. (Not Maeroiiu F. Cnvier.) 

 HkiHotciurtu Obat, Cat. Ham. Brit. Hna. 1813, 195 ; Ann. &. Mag. Nat. Hiat. 3d aer. xz, 1867, 886. (Type 



Soiiiru$ UpaobUs Bljih.) 

 Bkeinro»ei»rtu Gray, Ann. & Mag. Nat. Hist. 3d aer. zx, 18(n', 272. (Type Sciitm macroHt Gray.) 



Generic Ciiabs. — Skull short, very broad, especially interorbitally,and the 

 cranial portion greatly expanded ; postorbital processes terminating in a long, 

 slender point, directed posteriorly (and more or less outwardly) and decurved; 

 malar bone slender, the plane of its expansion nearly vertical ; anteorbital 

 foramen a narrow vertical slit, opening far in advance of the first premolar ; 

 upper grinding-teeth four or five, the first premolar (when two are present) 

 very small; muzzle short, nasals greatly narrowed posteriorly; ears well devel- 

 oped, well clothed, sometimes tufted, especially in winter; tail long, generally 

 as long as or longer than tlie body, broad, the long hairs spreading laterally ; 

 nail of pollex rudimentary; pelage generally full and soft, but sometimes 

 more or less rigid ; coloration variable, but never with well-defined black 

 stripes on the dorsum ; size generally large; no cheek-pouches, and uo lateral 

 membrane connecting the fore and hind limbs. 



The true arboreal Squirrels are at once easily distinguishable from the 

 Flying Squirrels by the absence of the membranous expansion along the 

 sides of the body as well as by numerous other very obvious differences. 

 They differ from Tamias in the form and position of the anteorbital foramina, 

 the broader and less tapering muzzle; in the greater verticality of the plane 

 of the malar bone; in the greater convexity of the dorsal outline of the skull; 



* See Agoaaiz, Nomeuclator Zuolugieua, Mamui. p. 19. 



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