170 NORTH AMERICAN MUSTELID^. 



and last premolar of Mustela martes and M. americana holds 

 good, there is reason to presume that the same difference may 

 constantly obtain in the Minks, as held by Dr. Gray. In this 

 case, very curiously, it is the American animal which has the 

 larger molar, not the European . This could never have been 

 l^redicated by analogy; it illustrates the constantly recurring 

 lesson of the danger of this mode of reasoning in zoology, and 

 the necessity of appeal to observed facts in every case. All 

 the many skulls of -American Minks examined (about forty) 

 show the massive last molar with an inner moiety very much 

 larger than the outer, as against the opposite which is alleged 

 of the Old World species. A discrepancy in average size of 

 the American and European Minks is obvious ; but the differ- 

 ence is within the range of variation of the former. The white 

 upper lip, the rule in the European species, is the rare excep- 

 tion in the American. As far as external differences go, it 

 would be impossible to separate the two forms specifically ; 

 we could only predicate a geographical race upon the average 

 superior stature and generally dark upper lip of the American 

 form. Attending only to these superficial details, Mr. Allen * 

 came to the justifiable conclusion of the specific identity of the 

 two animals ; but had his able and pertinent discussion em- 

 braced consideration of the dental peculiarities, his views would 

 doubtless have been materially modified. I am unable to en- 

 dorse his general statement {loc. cit.) respecting the Lutreola 

 group, that "we have here again but one circumpolar and 

 widely dispersed species, with i)ossibly two continental or geo- 

 graphical races which may be more or less easily recognized". 

 For aside from the question of P. vison^ the P. sihiricus (see 

 foot-note), which Mr. Allen would bring into the same connec- 

 tion, is an entirely different species, to judge from the single 

 excellent specimen before me. In justice to this writer, however, 

 I should not omit to add that since his examination of the skulls 

 he has presented P. vison as a distinct species. 



The comparative diagnosis of P. lutreola and P. vison would 

 be as follows : — 



P. hitreolaA — Back upper molar small, quadrate, transverse, the inner 

 moiety scarcely larger than the outer [fide Gray]. Averaging smaller; 

 upper lip normally white. 



"^ Bull. Mus. Comp. Zool. i. 1869, pp. 175-177 — an article important as a 

 contribution to the jiresent discussion, and as satisfactorily showing that 

 the external characters supposed to distinguish two species do not hold. 



+ 1 introduce short notices of the two Old World species allied to P. visorij 

 as further contributions to the history of the group. 



