168 NORTH AMERICAN MUSTELID^. 



Skulls of L. vlson ordinarily range from 2.35 x 1.35 to 2.75 

 X 1.65,* but the extreme limits of variation are considerably 

 further apart than these. Mr. J. A. Allen t has tabulated and 

 discussed the variations according to geographical distribution. 

 1 present his article in full : — 



" Eighteen skulls from the northern parts of the continent, 

 mainly from Alaska, average 2.66 in length and 1.58 in width, 

 the extremes being, length, 3.02 and 2.30; width, 1.90 and 1.40. 

 Thirteen skulls from the highlands of Northeastern New York 

 average 2.40 in length and 1.34 in width, the extremes being, 

 length, 2,60 and 2.17. Three skulls from Pennsylvania (un- 

 doubtedly males) average 2.49 in length and 1.48 in width. 

 In the northern series, the sex of the skull is given by the 

 collector, whence it appears that the twelve males have an 

 average length of 2.81, and the six females an average length 

 of 2.48, showing a considerable sexual variation in size. Yet 

 the smallest males (2.64 and 2.63) fall below the largest female 

 (2.68), if the skulls are all correctly marked. None of the 

 other females, however, exceed 2.55, and only three of the 

 males fall below 2.70. In the New York series, the sex is not 

 indicated; but, judging from the proportion of the small to 

 the large skulls, the sexes are about equally represented in 

 the two series, but in the New York series there is a very 

 gradual decline from the largest to the smallest. The northern 

 series of eighteen is selected from a series of twenty-three; 

 the New York series of thirteen from a series of thirty. lu 

 each case only very old skulls were chosen, the immature 

 specimens in each case being thrown out in'order to have a 

 fair basis for comparison. The immature and middle-aged 

 specimens greatly predominate in the New York series, owing, 

 doubtless, to the species being more closely hunted there than 

 in the more unsettled districts of the far north. 



'* Taking these two series as a basis for a general compari- 

 son, there is indicated a considerable decrease in size from the 

 north southward, amounting to 0.26 in length and 0.24 in 

 width, or about one-tenth of the average size of the New York 



* A skull of the commoQ Ferret, P. fcetidns var. faro, before me, is almost 

 exactly of the former dimensions. Tame Ferrets' skulls I have examined 

 show a curious depression of the cranial portion — even a concavity of the 

 upper profile, which I have not observed in P. foctidus. A skull of the latter 

 measures 2.60 X 1.55. 



t Bull. U. S. Geol. and Geogr. Surv. Terr. vol. ii. no. 4, 1876, pp. 327, 328. 



