30 The Mammals of Colorado 
SUBORDER DUPLICIDENTATA 
With two pairs of incisors in the upper jaw; the second pair 
small and placed directly behind the larger pair; the enamel 
of the incisors extending right round, and not confined to the 
front surface; incisive foramina of the palate large and 
usually confluent; fibula ankylosed with the tibia, and articu- 
lating with the calcaneum. 
Family LEPORID^ 
Animals of moderate size, with long ears, elongated 
hind limbs, and short, recurved tails; skull somewhat com- 
pressed, with characteristic wing-shaped postorbital processes; 
facial aspect of the maxillaries perforated and reticulated; 
teeth more numerous than in any other family of rodents; 
incisors large, and upper ones grooved; premolars |; molars 
rootless with transverse enamel folds. 
A large family found throughout the world except in the 
Australian region; a recent reviser, Lyon, has divided it into 
ten genera, and five subgenera, of which five genera and five 
subgenera are North American; but Nelson, in his just 
published monograph, only recognizes four genera and two 
subgenera in North America. 
Key of the Genera 
A. Interparietal not distinct in adult; size of Colorado species, 
with one exception, large; hind foot about 6; some species 
change color in winter. Lepus, p. 30 
B. Interparietal persistent in adult; size of Colorado species all 
small ; hind foot about 4 ; never change color in winter. 
Sylvilagus, p. 44 
Genus LEPUS (Lat., meaning a hare) 
Lepus Linnaeus, Syst. Nat.,ed. 10, i., p. 57(1758). Type, Lepus 
timidus Linn. 
