VARIATION 24 Variation with Age 24 Secondary Sexual Variation 26 Individual Variation 28 Seasonal Variation 30 Variation in Coloration and Molt 30 Variations of Taxonomic Worth 44 DISTRIBUTION AND SPECIATION 54 HISTORY OF CLASSIFICATION 69 Chronological List (annotated) of Specific and Subspecific Names Applied to American Weasels 71 CHECK-LIST OF AMERICAN SPECIES AND SUBSPECIES OF THE GENUS MUSTELA 81 ARTIFICIAL KEY TO AMERICAN SPECIES OF THE GENUS MUSTELA 83 DIAGNOSIS OF THE GENUS 83 EXPLANATION OF SYSTEMATIC TREATMENT 84 SYSTEMATIC ACCOUNTS OF SPECIES AND SUBSPECIES 87 _Mustela erminea_ 87 _Mustela rixosa_ 168 _Mustela frenata_ 193 _Mustela africana_ 406 EXPLANATION OF CRANIAL MEASUREMENTS 417 TABLE OF CRANIAL MEASUREMENTS 418 LITERATURE CITED 442 INDEX 461 American Weasels By E. RAYMOND HALL INTRODUCTION The weasel's agility and speed take it in and out of retreats, over obstacles and across open places in amazingly rapid fashion and are responsible for the animal's actions being described as "quick as a flash." The common long-tailed weasel of the United States measures approximately a foot and a half in length, of which the tail comprises a third; but the round, slender body is scarcely more than an inch and a half in diameter. Brown above and whitish below in summer dress, the animal is sleek as well as lithe and graceful. It is easy to understand, therefore, why the Bavarian name _Schönthierlein_ (pretty little creature) and the Italian name _donnola_ (little lady) were bestowed upon it. The Spanish name is _comadreja_ (godmother). In the winter, in temperate and northern regions, the coat becomes pure white except for the black tail-tip. In this dress the correct name for the animal is ermine, a mammal whose fur is known to all and justly esteemed, especially for its luster in artificial light, where it is scarcely excelled in enhancing the beauty of gems and their feminine wearers.