CKEODONTA. 305 



i. e., with three elevated cusps and a posterior heel. Premolars with a lobe 

 behind the principal cusp. The canine teeth are directed forwards, and are 

 very close together, so that it is doubtful whether there were any incisors. 

 An ungual phalange of the typical species is strongly compressed. 



The humerus in this genus is distally expanded transversely, and the 

 margin is pierced by tlie humeral artery. The astragalus exhibits two 

 entire trochlear faces; the wider external and directed interosuperiorly, the 

 inner presenting superointeriorly. They are separated by an obtuse longi- 

 tudinal angle, and are little or not at all concave transversely. The form 

 is depressed. The head supports a single transverse convex facet for the 

 navicular, and, with the neck, is as long as the trochlear portion. 



In this genus the sectorial tooth of the lower jaw is of a very primitive 

 type, resembling especially inferior molars of marsupials of carnivorous 

 habits. This is seen in the close approximation of the anterior cusp to the 

 two immediately succeeding it, and in its relatively small elevation in com- 

 parison with the external cusp. The latter is much elevated in this genus. 

 The heel of the same tooth is low; its length is in direct relation to the size of 

 the species; that is, it is relatively shortest in the smallest species. The rudi- 

 mental sectorial cusps of the tubercular tooth in B. liaydenianus show that 

 ■ but few changes of form are necessary to connect the inferior dentition of 

 this genus with that of Oxycena. 



The longest known species of this genus is the D. protenus, from the 

 Wasatch formation of New Mexico. Three additional species were after- 

 wards discovered by Mr. J. L. Wortmau in the Wind River country of 

 Wyoming. The species range from the size of a mink to that of a coyote. 

 Their characters are as follows, as derived from the mandibular teeth: 



I. Inferior tubercular molar with the three anterior cusps well developed. 

 Length true luolar.s .0125 ; last molar narrow D. haydenianus. 



II. Inferior tubercular with rudimental cusps. 



* Inferior tubercular molar oval in outline, with a heel. 



Length true molars .025; last three premolars .035; last molar short J), altidens. 



Length true molars .019 — .020; last three premolars .036; last molar elongate 



D. protemis. 

 Length true molars .016 — .018; last three premolars .028^.030; last molar narrow. 



D. leptomylus. 

 20 



