VARIATION IX SKULLS OF MUSTELA AMERICANA. 89 

 GEOGRAPHICAL VARIATION IN THE SKULLS OF M. AMERICANA. 



Mr. J. A. AUeu has recently* given a table of measurement of 

 length and breadth of forty-six skulls of this species, prepared to 

 show the range of geographical variation. His results are here 

 reproduced, together with his critical commentary on the 

 specific validity of M. amerkana. It will be seen that he aban- 

 dons his former t position, and endorses the distinctive charac- 

 ters of the dentition of MM. martes, foina, and americana. 



The forty-six male skulls of this spec.es, of which measurements are 

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

 tude. A comparison of the average size of a considerable number from each 

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

 River, the largest, and also from the most northerly locality, have an aver- 

 age length of 3.39, and an average width of 2.07, the extremes being 3.50 and 

 3.3.5 in length and 2.12 and 2.02 in width. Nine skulls from the Yukon (prob- 

 ably mostly from near Fort Yukon) give an average length of 3.34 and an aver- 

 age 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 1.65. Eight skulls from the vicinity of Um- 

 bagog 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 1.63 

 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 ditfereuce between the largest and 

 the smallest, excluding the most extreme examples, is one-sixth of the dimen- 

 sions of the smaller and one-seventh of the size of the larger. 



The sexes differ considerably in size, relatively about the same as in Puto- 

 rius vison; but the above generalizations are based wholly on males, and in 

 each case on those of practically the same age, only specimens indicating 

 mature or advanced age being used. 



The series of fully one hundred skulls of this species contained in the 

 National Museum presents a considerable range of variation in details of 

 structure, involving the general form of the skull, the relative size of differ- 

 ent parts, and the dentition, especially the form and relative size of the last 

 molar. In a former paper, t-I had occasion to notice somewhat in detail the 

 variations in color our American Martens present, and the difficulty of find- 



* Bull. U. S. Geological and Geographical Survey of the Territories, vol. ii, 

 no. 4, pp. 328-330 (July, 1876). 



t Bull. Mus. Comp. Zool. Cambridge, i, pp. J 61-167 ,Oct. 1869). 



t " Mammals of Massachusetts ", Bull. Mus. Comp. Zool. vol. i, pp. 161-167 

 (Oct., 1869). 



