SCIURID^— SPEBMOPniLUS. 



823 



of Arctomys. As far as can be judged from the characters afforded by the few 

 mandibular rami, from which as yet they are in the main only known, they 

 more resembled, at least in dentition, the existing species of Arctomys and 

 Sciurus ihan those of Cynomys, or the heavier-toothed forms of Spcrmophilus. 



As regards their present distribution, the Spermophili are confined mainly 

 to the colder portions of the northern hemisphere, and are numerously and 

 about equally represented in North America and the colder parts of the Old 

 World. All the Old World forms, with one exception (jS. everamami of North- 

 eastern Asia), are short-tailed forms, while the American species, with two 

 or three exceptions, are long-tailed, and approach more nearly to Sciurus and 

 Tamias than do those of the Old World. Several of the species range as far 

 westward as Central Europe, and are more or less numerous thence eastward 

 to the eastern shores of Northern Asia. In North America, none occur east 

 of tlie plains and prairies of the central portion of the continent, ranging 

 thence westward to the Pacific coast. The genus has representatives from 

 the shores - '' the Arctic coaBt southward to the plains of Northern Mexico. 

 All of the known species, except one, have representatives within ihe United 

 States, this being the S. annulatus, known as yet from a single specimen (of 

 which the locality is authentic) from Colima, Western Mexico. Another, 

 however (S. empetra), only just reaches our northwestern border, while no 

 less ^):xn three (S. mexicantu, S. spihsoma, and S. grammurus) are known to 

 occur onsiderably beyond the noi-thern boundary of Mexico. Only about 

 onc-fouith of the whole number of species are found nt any one locality. 



It may be further noted that the ^^elage of all of the southern species 

 consists of rather coarse, harsh, stiff hairs, generally flattened and grooved on 

 the outer surface, with very little or no under fur, especially in summer ; 

 while all the northern and alpine species, with one exception (S. franklini), 

 have a soft, thick, furry pelage, with abundant under fur. In respect to 

 geographical variation, there is, as a rule, a decided decline in size southward 

 in individuals of the same speciex, with quite often an appreciable increase 

 in the size of the ears. In respect to seasonal variations, the pelage is every- 

 where softer and heavier toward winter, with the soles quite fully clothed, 

 while in summer they are generally more or less naked. All the northern 

 species are known to pass the colder portion of the year in a stat« of hiberna- 

 tion. Southward, the period of hibernation is of course much shorter, while 

 the most southern forms continue more or less active throughout tiie winter. 



