once while the remainder of the coat was undergoing two molts. My inconclusive data lend but little support to this possibility. The difference in pattern of color between specimens taken in autumn and spring is known to some fur-trappers of my acquaintance who have suggested that molt occurs in spring, whereas the individual hairs change color in autumn. Reference to plate 39 will show how gross comparisons might lead one to this erroneous explanation of the color change. As to time of molt: In eight subspecies of _Mustela frenata_, namely, _noveboracensis_, _occisor_, _primulina_, _spadix_, _longicauda_, _arizonensis_, _nevadensis_ and _effera_, material is available to indicate that the autumnal molt begins in October and is completed in November, and that the spring molt occurs in March or April. A condensed list of specimens providing basis for this statement is as follows: _M. f. noveboracensis_: 26 specimens in transitional pelage taken in autumn and 14 taken in spring; _M. f. occisor_: One topotype has acquired one-fifth of the winter pelage on October 22, 1896; _M. f. primulina_: 2 in November, one in March, and 2 in April are in process of change; _M. f. spadix_: 6 autumnal specimens and one in April show pelage change; _M. f. longicauda_: 7 autumnal specimens and one in April show pelage change; _M. f. arizonensis_: 12 specimens in autumn and 3 in spring are in process of molt; _M. f. effera_: One November-taken male has acquired four-fifths of the winter coat and another taken on April 21 at Fort Rock, Oregon, is half finished with the spring molt. It may be added that no marked difference in time of either autumnal or spring molt is apparent as between the more northern and more southern localities from which the mentioned specimens come. With more complete material I would expect to find a difference in this regard. The material of the other, more southern, subspecies of _Mustela frenata_ has not been adequate to show the time of molting or the number of molts which occur in one year. Animals in the northern part of the range of _Mustela frenata_ acquire a white winter coat, whereas those in the southern part acquire a brown winter coat, and in an intervening area the winter coat may be either brown or white. By plotting on a map the localities of capture of all specimens examined in the winter coat, it was possible to outline this intervening area as shown in figure 10 on page 37. However, Dearborn (1932:36) shows that in Michigan some animals have a brown coat in winter at places farther north than figure 10 shows to be the case. Hamilton's (1933-306) map for New York shows the same to be true in that state. Accordingly, the boundaries of the area shown in figure 10, in which both brown and white long-tailed weasels occur in winter, are known to be only approximate; with full information available the belt would be represented as wider.