1881.] 1* * LCope. 



Measurements of incisor. M. 



r anteroposterior 012 



Diameters of crown } transverse ; 020 



'.vertical 020 



^. ^ (-anteroposterior 012 



Diameters of root \ ^ r... 



\ transverse 014 



This incisor is very different from the kind seen in Loxolophodon. Mr. 

 Osborne has shown that genus to have tliese teetli with compressed two- 

 lobed crowns, a type unlinown elsewhere among Mammalia.'^ 

 PERISSODACTYLA. 



In a paper on the "homologies and origin of the molar teeth of the 

 Mammalia Educabilia, " published in March, 1874, f I ventured the gene- 

 ralization that the primitive types of the Ungulata would be discovered to 

 be characterized by the possession of five-toed plantigrade feet, and tuber- 

 cular teeth. No Perissodactyle or Artiodactyle mammal was known at 

 that time to possess such feet, nor was any Perissodactyle known to 

 possess tubercular teeth. Shortly after advancing the above hypothesis, I 

 discovered the foot structure of Coryphodo7i, which is five-toed and planti- 

 grade, but the teeth are not of the tubercular type. For this and allied 

 genera, I defined a new order, the Amblypoda. and I have published the 

 confident anticipation that genera would be discovered which should possess 

 tubercular (bunodont) teeth. This prediction has not yet been realized. 

 I now, however, record a discovery, which goes far towards satisfying the 

 generalization first mentioned, and indicates that the realization of the 

 prophecy respecting the Amblypoda, is only a question of time. 



In 1873,11 I described from teeth alone, a genus under the name of 

 Phenacodus, and although a good many specimens of the dentition have 

 come into my possession since that date, I have never been able to assign 

 the genus its true position in the mammalian class. The teeth resemble 

 those of suilline Ungulates, but I have never had sufficient evidence to 

 permit its reference to that group. Allied genera recently discovered by 

 me, have been stated to have a hog-like dentition, but that their position 

 could not be determined until the structvire of the feet shall have been as- 

 certained. § 



In his recent explorations in the Wasatch Eocene of Wyoming, Mr. J. 

 L. Wortman was fortunate enough to discover nearly entire skeletons of 

 Phenacodus priiiKBmis, and P. mrtmani, which present all the characters 

 essential to a full determination of the place of Phenacodus in the S3'stem. 

 The unexjiected result is, that tliis genus must be referred to the order 

 Perissodactyla, and that with its allies, it must form a special division of 

 that order corresponding in the tubercular characters of its teeth with the 



* A Memoir on Loxolophodon and Uintatherium. By H. Osborne, 

 t Journal of the Acadenij' of Natural Sciences, Philadelpliia. 

 |l Pal Eeonto logical Bulletin Xo. 17, Oct., 1873, p. 3; also. Report G. M. Wheeler, 

 U. S. Engineers Expl. W. 100 Mer., iv, p. 174r-1877. 

 ^ Proceedings Amer. Philos. Society, 1881, p. 495. 



