From _murica_, _invicta_ of corresponding sex differs in being larger in every measurement taken; males average 17 per cent larger in cranial measurements, 13 per cent larger in dental measurements and are 83 per cent heavier; corresponding percentages for females are 11, 9 and 20. Exception must again be made for the anteroposterior diameter of the inner lobe of the last upper molar which is less in females, and only slightly more in males. In males of _invicta_ the tympanic bullae are longer in relation to the basilar length. From the geographically remote _cicognanii_, skulls of both males and females of _invicta_ are to me individually indistinguishable. There is, nevertheless, an average difference not apparent to the eye between skulls of males. If the length of the tooth-rows be taken as a standard (100 per cent), the rostrum, of _invicta_, as measured across the lacrimal processes is broader (89 rather than 84 per cent) but the width across the fourth upper premolars is less, 94 rather than 97 per cent of the length of the tooth-rows. Since the skull of _invicta_ closely resembles that of _cicognanii_, it follows that _invicta_ differs from _richardsonii_ and _bangsi_ in about the manner described in the account of _cicognanii_. _Remarks._--Animals of this subspecies in advance of the present study generally were recorded in the literature under the name _Mustela cicognanii_. The difficulty in distinguishing individual specimens of _invicta_ on morphological grounds from those of the geographically remote _M. e. cicognanii_ should not be taken to indicate that the populations do not differ appreciably. Actually they differ in several characters although in no one of these is the degree of difference sufficient to allow of using it alone as a certain means of diagnosis. In _invicta_, as compared with _cicognanii_, the light-colored underparts are wider in relation to the dark-colored upper parts and the tail is longer by 4 per cent relative to the head and body. Given a population of each of the two subspecies, in which the skull is of the same mass, the hind feet are longer in _invicta_, there is more sexual dimorphism in size, and the anterior part of the skull differs in some particulars as just described in the comparison of the skull of _invicta_ with other forms. Nevertheless, each of these differences is of an average sort. Therefore, and because overall size is about the same in the two subspecies concerned, one or a few specimens from, say, central Idaho, can be distinguished from animals from western Pennsylvania only with difficulty, if at all. The close resemblance of skulls of _invicta_ and _cicognanii_ may be a function of their living at approximately the same latitudinal position in a climate that has marked seasonal variation.