ARTIFICIAL KEY TO AMERICAN SPECIES OF THE GENUS MUSTELA
Reading edition
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A Length of upper tooth-rows less than 20 mm. in males and 17.8 mm. in females.
B Postglenoid length of skull more than 47 per cent of condylobasal length.
C Tail without a black pencil and with at most a few black hairs at extreme tip; in both sexes mastoid breadth ordinarily exceeds breadth of braincase,
Mustela rixosa, least weasel, p. 168
C' Tail with a black pencil; in females mastoid breadth ordinarily exceeded by breadth of braincase,
Mustela erminea, ermine, p. 87
B' Postglenoid length of skull less than 47 per cent of condylobasal length.
D Tail with distinct black tip; midventral line white, yellowish, orange, not same color as upper parts; p2 present; thenar pad on forefoot absent,
Mustela frenata, long-tailed weasel, p. 193
D' Tail without black tip; midventral line same color as upper parts; p2 absent; thenar pad on forefoot present,
Mustela africana, tropical weasel, p. 406
A' Length of upper tooth-rows more than 20 mm. in males and 17.8 mm. in females.
E Abdomen all white; face with blackish mask; m1 lacking even a trace of a metaconid; distance between upper canines more than width of basioccipital as measured between foramina situated midway along medial sides of tympanic bullae,
Mustela nigripes, black-footed ferret.
E' Abdomen dark brown, like back; face uniformly brown without blackish mask; m1 with incipient metaconid; distance between upper canines less than width of basioccipital as measured between foramina situated midway along medial sides of tympanic bullae,
Mustela vison, mink, American mink.