1^0.2.] TROUESSART ON REVISION OF THE GENUS SCIURUS. 303 



closely with their geographical distribution. We recur to Gervais's 

 classification in attempting in our turn to subdivide the genus into a 

 certain number of natural groups which we call subgenera. Whenever 

 possible we have retained the prior names of other authors, such as 3Ia- 

 croxus, Funamhulus, Geosciurus, Spermosciurus / but we differ with most 

 late zoologists in their limitation and characterization. Since only sub- 

 generic distinctions are in jjoint, little inconvenience results from utiliz- 

 ing names usually considered as mere synonyms of Sciurus or of Xerus. 



The characters which can be used to the best advantage are the na- 

 ture of the pelage, the shape of the skull and number of premolars, the 

 relative length of the tail, and others of the same kind. 



As to the ear-tufts, used by Gray to separate the true Sciuri from his 

 Blacroxi, they are of no account, since species closely related in all other 

 respects difler only in this feature, which in others, again, dei^ends upon 

 season.* 



In certain intertropical species the shape of the tail is equally variable 

 according to season, being cylindrical in the rainy season, corresponding 

 to our winter, but becoming distichous in summer, or in the rutting 

 season. There are, however, many species in which the tail is always 

 cylindrical, while in others it becomes bushy but not distichous. 



The pelage is equally variable according to season, as in mammals at 

 large. The African Squirrels are nearly all remarkable for the harshness 

 and bristly structure of the pelage, which is generally little mixed with 

 under-fur, if at all, and thinly scattered on the belly, which is almost 

 bare, at least in the warm season. The species of this region, moreover, 

 require renewed study before the actual value of many of them and the 

 limits of the genus Xerus can be determined. Certain South American 

 species approach them in the stiff, bristly character of the pelage. 



Upwards of 200 species of squirrels have been described ; in our Cat- 

 alogiie des Mammiferes and in the following Synopsis we reduce this figure 

 to about 80. This number itself is probably too large, and will be in 

 the end considerally reduced. A total of about 60 perfectly distinct 

 species seems to us to be still nearer the truth ; and this will iDrobably 

 be attained when the Asiatic and African species shall have been as 

 thoroughly studied as those of America. 



Genus Sciiiriis L. 



Chars. — Two upper premolars, the first small, often deciduous or want- 

 ing ; one under premolar. Limbs free; form fitted for agility. Skull 

 with more or less salient post-orbital i^rocesses ; infra-orbital foramen 

 opening in front of the anterior fork of the zygoma ; no cheek pouches. 

 Ears and tail varying with the species. Three or four pairs of teats in 

 most species ; only two in the subgenus Xerus. Pelage varying in the 

 different subgenera. Dental formula:!. \'\ ', M. J^ (or ^). 

 [* For example, among American species, the allegc'd»SctH)-«!.c«s^rt/(o»(>^«8ofBaird.—C.] 



