318 

 VULPBS ALOPEX ET YAKS. 



In the Common Fox of North America, we meet with a range of color- 

 variation, irrespective of locality, somewhat akin to that seen in Canis 

 lupus. The prevalent tendency, however, is toward melanism, which 

 tendency is much more strongly developed in the colder than in the 

 warmer latitudes. Frequently, individuals of the melauistic type occur 

 in litters of the common variety. The varying degrees of melanism 

 occurring in this species have given rise to several commercial varieties, 

 which have received at the hands of naturalists systematic designations, 

 and been regarded more or less generally as valid species. Generally, 

 these melanistic varieties are more fully furred, with larger and heavier 

 tails, than the common form. The difference in the fineness and soft- 

 ness of the fur is recognized to such an extent by furriers as to greatly 

 affect the price of the skins, the so called "Silver" and " Cross" furs 

 being considered far more valuable than the fulvous type. 



The so-called " Cross Fox" ( Vulpes " decussatus") is more or less frequent 

 as far south as Northern New England and Northern New York, and 

 throughout the more elevated portions of the great Eocky Mountain 

 plateau, where it constitutes a large proportion of the representatives 

 of the so-called Vulpes "macrurus". More rarely, the Black or so- 

 called " Silver Fox" (Vulpes u argentatus") is met with over the same 

 regions, becoming frequent in the higher parts of the Eocky Mountains* 

 and northward. The fulvous form seems, however, to be generally the 

 more prevalent form throughout the range of the species. To the south- 

 ward, it is the form exclusively met with ; but near timber-line in the 

 Eocky Mountains, and throughout the "fur countries", it seems to be not 

 much more frequent than the melanistic forms. 



With this tendency to great variability in color, we meet, as usual in 

 such cases, a great variation in size. In the present case, the variation in 

 color may be properly regarded as geographical, through an increasing 

 tendency to melanism northward. The variation in size is also chiefly 

 of the same character, the size uniformly increasing toward the north, 

 as shown by the subjoined table of measurements. A glance at this 

 table shows at once the nature of this variation. The largest specimens 

 come from the Aleutian Islands and Alaska ; the smallest from Essex 

 County, New York, which is the most southerly locality well represented 

 in the collection. 



A series of nine skulls from Alaskan localities range in length from 

 5.70 to 6.20, five out of the nine having a length of 6.00 to 6.20 (two 

 6.15 and two 6.20), and give an average of 5.98. In another series of 

 eighteen from the Mackenzie Eiver district (mainly from Fort Ander- 

 son), the range is from 5.55 to 6.10. Only one, however, exceeds 6.00, 

 and three only reach this size, the average being 5.80. These series 

 consist about equally of the so-called "Silver" and common fulvous 

 varieties, and, as may be seen from the table, there is no material dif- 

 ference in size between the two so-called varieties. 



A third series of nine skulls, of the so-called "macrurus", chiefly from 

 the Upper Missouri country (including two, however, from the Pacific 

 slope), ranges from 5.40 to 6.00, with an average of 5.75. Two only 

 reach 6.00, and two only fall as low as 5.50. Hence the series forms a 

 third appreciable step in the southward decrease in size. Though the 

 latitude is much less, the elevation of the region is much greater than 

 that of the localities more to the northward. With a similar altitude, 

 the decrease would have been more marked, as is proven by the series 



*See Bulletin Essex Institute, vol. vi, p. 54. 



