i88 The Mammals of Colorado 
This order is divided into two suborders for the terrestrial 
and marine forms respectively, and comprises altogether 
eleven families. Only four of these are represented in the 
Colorado fauna, the marine forms naturally being absent, 
as well as the Civets (ViverridcE) , the Aard Wolf {Protelidce), 
and the Hyenas (HycenidcE), all of which are confined to the 
Old World. 
Key of the Families 
A. Plantigrade or semi-plantigrade; five toes to both limbs; 
claws non-retractile. 
a. Plantigrade to nearly digitigrade ; tail never annulated ; 
molars |. Mustelidae, p. i88 
b. Plantigrade or semi-plantigrade ; tail moderate or long, annu- 
lated; molars |. Procyonidae, p. 218 
c. Plantigrade with naked soles; tail very short, almost rudi- 
mentary; molars f. Ursidae, p. 222 
B. Digitigrade; complete toes, 4 on fore limbs, 5 on hind; claws 
blunt and non-retractile. Canidae, p. 233 
C. Digitigrade ; toes, 5 on fore limbs, 4 on hind ; claws curved, sharp, 
and retractile. Felidae, p. 251 
FamUy MUSTELIDiE 
This family contains the Otters, Weasels, Badgers, and 
Skunks, and cannot be easily characterized by external 
characters. Both limbs with five toes and with flat nails or 
non-retractile claws; skull with the auditory bullae depressed, 
uninflated, and undivided as in the UrsidcE but with no 
alisphenoid canal; post-glenoid process considerably pro- 
duced and curved round the glenoid fossa so as to hold the 
condyle of the lower jaw very tightly and prevent the mandible 
being easily pulled away from the cranium; dentition with 
molars the inner tubercular portion of the single upper 
molar always longer in an antero-posterior direction than the 
cutting external portion. 
Key to Subfamilies and Genera 
A. Feet short and rounded; toes fully webbed; habits aquatic 
{LiitrincB). Lutra, p. 189 
