234 The Mammals of Colorado 
never surrounded by a ring of bone; auditory bullae inflated 
but not divided into two chambers; alisphenoid canal present; 
dentition with four premolars on either side above and 
below; upper carnassial with two cusps, the anterior back- 
wardly directed one being the larger, the posterior forming a 
compressed ridge, while there is also a small inner lobe at the 
anterior end of the tooth; the first upper molar large and 
broader than long, with the cusps on the external border; 
the second upper molar similar but smaller; the lower carnas- 
sial a large tooth, with anteriorly a well-developed bilobed 
blade, of which the hinder cusp is the larger; onto this latter 
hangs a small inner tubercle, while the posterior part of the 
tooth forms a well-marked tuberculated heel. 
Key of the Genera 
A. Tail longer and more bushy, more than J the length of the body ; 
skull without a frontal sinus; postorbital processes 
convex. 
a. Muzzle shorter ; tail with a mane of stiff black hairs. 
Urocyon, p. 234 
b. Muzzle longer; tail without mane. Vulpes, p. 236 
B. Tail shorter and less bushy, less than ^ the length of the body; 
skull with a frontal sinus, and postorbital processes 
convex. Canis, p. 240 
Genus UROCYON (Grk. oura, tail, -|- kuon, dog) 
Urocyon Baird, Mamm. N. Am., p. 121 (1857). Type Canis 
virginianus Erxleben. 
"Tail w^th a concealed mane of stiff black hairs without any 
soft fur intermixed ; muzzle short; temporal crests widely separated. 
Upper incisors scarcely lobed; postorbital processes bent but httle 
downward, the anterior edge turned up, a longitudinal shallow 
pit at its base. Supplementary tubercle on the lower sectorial. 
Under jaw with an angular emargination below." Baird, I. c. 
Dentition: i. f ; c. {; pm. f ; m. f X 2 = 42. 
Pupil elhptical. 
This genus is found exclusively in North America, but 
does not have the extreme northern range of Vulpes, being 
a much more southern animal, ranging from Guatemala 
