Cope.] 180 [Dec. 16, 



Phenacodus puercensis Cope. Proceeds. Amer. Philos. Soc. 1881, p. 492. 

 An abundant species, represented by twelve mandibular rami in the 

 collection, and by a nearly entire skeleton with perfect skull. 



Phenacodus apternus, sp. nov. 



Three rami, each of which supports the true molar teeth, indicate this 

 species. The oval form of the posterior molar is due to the shortness of 

 the heel, and the large size of the internal median tubercle, which pro- 

 jects inwards, giving a convex outline to the interior side of the crown. 

 The external tubercles of all the true molars wear into crescents ; and the 

 anterior inner is more robust than the posterior inner. 



Phenacodus macropternus, sp. nov. 



This species is apparently rare, being represented by only one man- 

 dibular ramus, which supports the posterior three molars, and a possible 

 second ramus with molars iv and v. The first and second true molars 

 are much like those of P. vortmani, but the third is relatively larger, and 

 has an especially elongate heel. In P. vortmani the last molar is con- 

 stricted, and narrower than the penultimate. In P. macropternus there 

 is a weak external, and no internal cingulum. The tubercles of the last 

 two molars are quite regularly conical, while the external pair of the first 

 molar, wear into crescents. Smaller than the P. vortmani. 



Phenacodus brachypternus, sp. nov. 



Three mandibular rami are the only specimens of this species found by 

 Mr. Wortman in the Big-Horn region. They all display the fourth pre- 

 molar, which has the characters of this genus, as distinguished from 

 Mioclcenus. The species is materially smaller than the P. vortmani, and 

 its last inferior molar is intermediate between those of the latter and the 

 P. apternus, in form. Both the internal and external intermediate tuber- 

 eles are very full, and give the tooth posterior width. The posterior or 

 fifth tubercle is large, and gives the posterior outline of the crown a tri- 

 foliate form. The posterior median tubercles of the M. II and I, are well 

 marked. The molars gradually increase in size forwards, and the fourth 

 premolar is longer than any of them, and rather narrow. The heel of the 

 P-m. Ill is short and wide. On the true molars a weak external cingu- 

 lum. Enamel slightly wrinkled. 



Phenacodus zuniensis Cope. Proceeds. Amer. Philosoph. Society, 

 1881, p. 462. 



Mr. "Wortman obtained eleven mandibular rami of this species, in only 

 one of which are the premolars preserved. Excepting the P. laticuneus, 

 this is the smallest species of the genus. The molars have much the ap- 

 pearance of those of the Mesodont genus Hyopsodus, but may be dis- 

 tinguished by the size of the posterior median tubercle. The second 

 true molar is the widest tooth, and the last molar is rather elongate, and 

 its cusps are not exactly opposite to each other. The cusps of the molars 



