FAMILY. 



SCIURIDAE. 



Molars ^rj or ^ri rooted or rootless. No ante-orbital foramen in the anterior root of the zygoma, or else small and rounded. 

 Tibia and fibula distinct. 



The family of Sciuridae as above constituted, and embracing the sub-families Sciurinae, Myox- 

 inae, and Castorinae, has an extensive range : the first, throughout the world ; the second, in 

 Europe, Asia, and Africa ; the third, in Europe, Asia, and North America. The most promi 

 nent characters by which the sub-families may be distinguished are as follows : 



55 

 4^4* 



Sciurinae. A distinct post-orbital process. Molars rooted, 

 Myoxinae. No post-orbital process. Molars rooted, ~. No coecum. 

 Castorinae. No post-orbital process. Molars rootless, ^, (^ Aplodontia.) 



SUB-FAMILY SCIURINAE. 



6-6 



Molars, 717, (the anterior upper sometimes deciduous,) rooted; all nearly equal in size, except the anterior upper when there 

 are five. A distinct post-orbital process of the frontal bone. The infra or ante-orbital foramen very small, not piercing the 

 broad plate of the zygoma, but anterior to this. 



The Sciurinae constitute a very natural group as characterized above, although there is a 

 great diversity of appearance between the delicately formed and graceful arboreal true squirrels, 

 at one end of the series, and the clumsy, squat, terrestrial marmots at the other. The compo 

 nent genera, Sciurus, Pteromys, Tamias, Spermophilus, and Arctomys, are all fully represented 

 in North America by more species than are found in other parts of the world ; only one genus, 

 Pteromys, having more species elsewhere than here. 



The muzzle is generally broad, owing to the development of the frontal and nasal bones. 

 The acute process of the orbital edge of the frontal, which, pointing backwards, forms the 

 hinder upper boundary of the orbit, is a peculiarity only found elsewhere, if I am not mistaken, 

 among the hares. The palatine surface is large and broad, on the same plane from behind the 

 incisors ; the incisive foramina far forwards and entirely in the intermaxillaries, seldom if ever 

 passing backwards into the maxillary, which does not send forward a thin plate. The posterior 

 margin of the palate passes considerably behind the last molar. There are two palatine fora 

 mina, either in the palato-maxillary suture or behind it. 



The zygomatic process of the upper maxillary is a broad thin plate which rises obliquely from 

 the bone, is cylindrically concave in front, and has a broad concave notch at its lower edge, the 

 postero-inferior edge of which is on a level with the bottom of the palate internally, but exter 

 nally rises somewhat above this level ; superiorly, this palate reaches up nearly to the top of 

 the skull, articulating on the edge of the muzzle with the intermaxillary. There is, usually, 



