loO BULLETIN OF THE 



but few mammalogists have come to recognize these variations as man- 

 ifestations of general laws, and we are consequently scarcely surprised 

 at the glaring inconsistencies into which even our best authorities are 

 frequently betrayed, they at times assigning to these several variations 

 their true character, and again, in apparently equally clear cases, con- 

 sidering them as indications of specific diversity. It thus happens that 

 species are still not unfrequently based solely on differences that are but 

 individual peculiarities, from these differences being first detected in com- 

 paring specimens from widely separated districts, whereas they are not 

 different from variations presented by occasional specimens of the same 

 species at any given locality. Oftener still, perhaps, species are founded 

 on slight geographical variations, either solely or in connection with ex- 

 ceptional individual peculiarities, or on differences depending upon age. 

 A remarkable instance of this latter kind seems to have occurred in 

 our SoreciJce, and especially in Blarina, where no less than eight at 

 present currently received species are apparently based on one. Imper- 

 fectly understood sexual variations, associated with other differences, in 

 some cases render the complication still greater. This occurs in the 

 Mustelidee, where the female is found to be very much smaller than the 

 male in almost or quite all species when the sexual differences are well 

 known. In the weasels the large amount of this difference seems to 

 have thus far generally escaped notice, especially by American writers. 

 As wide a range of variation, aside from the sexual, obtains in these as 

 in their near allies, the mink and the marten. In this group, differ- 

 ences in size and in the relative length of the tail as compared with the 

 body — the latter an extremely variable elemeut — have been taken 

 as important specific distinctions, and on these grounds alone some five 

 species (so called) appear to have been based on two. 



In respect to the differences that have been claimed to separate spe- 

 cifically the Old and the New World representatives of those species 

 we in this paper consider identical, only those of very slight importance 

 have as yet been adduced ; they are only such as might be anticipated 

 to occur when, as has repeatedly happened, the comparisons have been 

 made between only a few specimens known to have been collected at 

 localities widely differing in latitude, and hence in climatic conditions, 

 and at different seasons of the year. More frequently, however, the 

 exact origin and history of the specimens compared appears to have 

 been wholly unknown. In no case are the differences greater, but 



