74 SCOTT — ON THE SELENODONT AKTIODACTYLS. [March 18, 



Uinta Selenodonts has led is the very unexpected conclusion that, 

 with the possible exception of the Oreodonts and Agriochoerids, all of 

 the strictly indigenous North American Seie?iodonts are derivatives 

 of the Tylopodan stejn. The true Ruminants (Pecora) are an Old 

 World type and did not reach this continent till late Miocene times, 

 but the Tylopoda underwent an expansion and differentiation in 

 America comparable to that of the Pecora in Europe, of which they 

 took the place here. This conclusion was long ago suggested, with 

 wonderful insight, by Riitimeyer, but as he did not discuss the 

 question and brought forward no evidence in support of his views, 

 the suggestion never attracted the attention which it so well de- 

 served. The White River forms, Leptomeryx, Hypertragulus, Hypi- 

 sodus and Frotoceras, have long baffled the investigator who 

 attempted to determine their true systematic position, but it has 

 now become exceedingly probable that they are all variants of the 

 Tylopodan type, the main line of which is represented in White 

 River times by the genus Poebrotherium, whose position has long 

 been recognized as ancestral to the modern camels and llamas. It 

 should be added, however, that this somewhat surprising result has 

 been much strengthened and confirmed by far more complete 

 material of Leptomeryx and Hype7'tragiiius than had previously 

 been known. This new material, which was gathered at various 

 times by Messrs. Hatcher and Gidley, makes the Tylopodan affini- 

 ties of these White River genera much more conspicuous than any 

 one had imagined. In the extended paper which is now in course 

 of preparation these newly obtained specimens will be described 

 and figured in comparison with their forerunners of the Uinta. 



Parameryx Marsh. 



Amer. Jour. Sci., third series, Vol. xiv, p. 364 {nomen nudiwi). 

 Ibid., Vol. xlviii, p. 269. 



In this genus the dentition is complete, I. f , C. \, P. |, M. f and 

 there are no diastemata. The incisors and canines are small, the 

 premolars simple and trenchant and the molars very brachyodont and 

 composed of four crescents. The skull is exceedingly like that of 

 Poebrotherium, but has a shorter muzzle, a less capacious cranium, a 

 more widely open orbit and a very much smaller tympanic bulla, 

 which is not filled with cancellous tissue. The ulna and radius are 

 separate, at least in young individuals ; the manus consists of four 



