Weasels 
193 
genera of the family, are subject at times to a parasite which 
locates in the sinus of the frontal and may cause much dis- 
tortion of that part of the skull, and thus mislead the student 
if he happens to fail to notice the cause. 
FIG. 62. BLACK-FOOTED FERRET, PutoHuS nigHpeS 
Skull showing dentition x i J 
Key OF THE Species 
A. Size large, length of adult male, 19.5 ; body rather heavy for a 
weasel; does not turn white in winter; color bufEy, feet 
and band across face black; skull large and massive, with 
prominent postorbital process and pronounced post- 
orbital constriction. P. nigripes, p. 194. 
B. Size medium; turn white in winter. 
a. Larger, total length of males, 17.75, of females, 15.25; color 
in summer light brown above ; postorbital constriction 
very marked in adult animals. P. longicauda, p. 195. 
b. Smaller, total length of males, 16 or less, of females, 14; color 
in summer dark brown above ; postorbital constriction 
not so great as in preceding; but still well marked. 
P. arizonensis, p. 196. 
C. Size small, total length, 9.5; turns white in winter. 
P. streatori leptus, p. 197. 
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