CRANIAL VARIATION IN PUTORIUS VISON. 167 



lighter as it advances in years, and that the white blotches or 

 spots are of greater size and distinctness in the old than in the 

 young. The fur of a young Mink (under three years) when 

 killed in season is very handsome : its color is often an almost 

 pure black. The skin is thin and pliable, approaching nearly 

 to the papery consistency of that of the Martin. When aged, 

 the hide is thick and the color more rusty. The summer pelage 

 is short, but tolerably close, and is of a reddish brown color, 

 and the tail, though still possessing black hairs, shews dis- 

 tinctly the under-fur of a decidedly rusty hue. Its feet are 

 rather pointed and not large. Its legs are short but muscular, 

 and its track in the snow is easily distinguished from that of 

 the Martin, whose longer and well-covered paws do not sink so 

 deeply. Indeed, when the snow is at all deep and soft, the 

 Mink makes a regular furrow, similar to that made by an Otter 



under like circumstances, though of course smaller 



I am strongly inclined to the opinion that there is only one 

 species of Mink on this continent, and consider it highly prob- 

 able that the P. Nigrescentes of And. & Bach, are merely 

 common Minks under three years of age. I have seen numbers 

 of skins here of exactly the same color, size, and furring as 

 those described under that head in Prof. Baird's work on North 

 American Mammals, which were simply young P. visones. This 

 gentleman also states that the American species of Mink never 

 has the edge of the upper lip white. I have never seen the 

 whole of that part so colored, but in one specimen now on my 

 table there is a white spot beneath the nostrils." 



To the above account of the variations in pelage must be 

 added another source of change in specimens, namely, the 

 fading by long exposure to the light. Some mounted individ- 

 uals which have been in the Smithsonian museum for about 

 twenty years are now bleached to a dingy white nearly all 

 over. 



The time that the Mink requires to attain full stature is seen 

 from the foregoing. As usual in this genus, the female aver- 

 ages considerably smaller than the male. 



Yariation in the skull of the MinJc. 



Having already given the principal characters of the skull 

 in treating of the subgenus Lutreola, it only remains to note 

 the variation presented by the present species. 



