328 



Measurements of thirty-seven skulls o/PuxoRius VISON. 



MUSTELA AMEBICANA. 



The forty-six male skulls of this species, of which measurements are 

 given below, are mainly from four or five localities differing widely in 

 latitude. A comparison of the average size of a considerable number 

 from each shows a well-marked decrease in size southward. Four skulls 

 from Peel Eiver, thelargest, and also from the most northerly locality, have 

 an average length of 3.39, and an average width of 2.07, the extremes 

 being 3.50 and 3.35 in length and 2.12 and 2.02 in width. Nine skulls from, 

 the Yukon (probably mostly from near Fort Yukon) give an average length 

 of 3.34 and an average width of 1.98, the extremes being 3.55 and 3.00 

 in length and 2.15 and 1.73 in width. Five skulls from Fort Good Hope 

 give an average length of 3.24 and an average width of 1.95, the 

 extremes in length being 3.37 and 3.15 and in width 2.05 and 1.73. Ten 

 skulls from the northern shore of Lake Superior average 3.14 in length 

 and 1.76 in width, the extremes in length being 2.23 and 3.02 and in width 

 1.89 and 165. Eight skulls from the vicinity of Umbagog Lake, Maine 

 (Coll. Mus. Comp. Zool.), average 2.96 in length and 1.72 in width, the 

 extremes in length being 3.10 and 2.73, and in width 1.85 and 1.50. Five 

 skulls from Northeastern New York average 3.02 in length and 1.61 in 

 width, the extremes being in length 3.10 and 2.92 and in width 1.68 and 

 1.50. There is thus a gradual descent in the average length from 3.39 to 

 3.02. and in width from 2.07 to 1.61. The largest and the smallest of the 

 series are respectively 3.55 and 2.92 in length. Several fall as low as 

 3.00, and an equal number attain 3.50. The difference between the 



