[ARTIFICIAL KEY TO AMERICAN SPECIES OF THE GENUS MUSTELA]
| PAGE | |
| 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. |
[DIAGNOSIS OF THE GENUS]
Genus Mustela Linnaeus
Weasels, Ferrets, Polecats, Minks
Genotype.—Mustela erminea Linnaeus.
Diagnosis.—Legs short; body relatively long; adults 190 mm. to 700 mm. in total length; skull ranging in basilar length from 16 to 70 mm.; facial angle slight; tympanic bullae greatly inflated (moderately in Lutreola), cancellous, and with paroccipital processes closely appressed to bullae; palate behind upper molars; dental formula:
I 3 C 1 P 2-3 M 1
-, -; -, -; -, ---; -, -;
i 3 c 1 p 3-2 m 2