AMERICAN RUMINANT-LIKE MAMMALS. 249 



to that followed by the Pecora and Tragulina the latter a 

 group which never reached America at all. 



It is this very parallelism of the Tylopoda with the Pecora 

 and Tragulina which has led astray so many students of the 

 peculiar North American selenodonts, myself among the num- 

 ber. We have continually been endeavoring to detect relation- 

 ships between these forms and the European ruminants and 

 chevrotains, where no such relationships existed, but only analo- 

 gies, parallelisms, or convergences. The truth appears to be 

 that the indigenous American selenodonts make up a natural 

 assemblage of forms which, with a remarkable degree of diversity 

 in size and structure, are yet all quite closely related among 

 themselves, but only distantly with the Old World types which 

 more or less resemble them. The group formed by the asso- 

 ciation of these American families is, in fact, so diversified 

 that a definition can hardly be framed for it ; but that is, of 

 course, no valid reason for refusing to recognize it as a natural 

 group. Just as the Pecora are typically Old World both in 

 origin and development, so the Tylopoda are typically North 

 American, and did not reach the eastern hemisphere till the 

 end of the Miocene or beginning of the Pliocene, and then in 

 very limited numbers, Camelus and its immediate forerunners 

 being the only known Eurasian representatives of the group. 



The late Professor Riitimeyer of Basle, one of the greatest 

 of palaeontologists, reached practically the same conclusion long 

 ago, though no American agreed with him. It is an excellent 

 example of his wonderful power of insight into a tangled prob- 

 lem of phylogeny that he should have discerned this fact, as I 

 believe it to be, at a time when the fauna of the White River was 

 but very imperfectly known and that of the Uinta had not yet 

 been discovered. Dr. Wortman, in his latest paper, seems to 

 have adopted Riitimeyer's views, though he does not explicitly 

 say so, and for the same reasons that have led me to change 

 my previous opinions, namely, the convincing power of the 

 Uinta genera, all of which seem to be converging into a com- 

 mon term with the primeval member of the main tylopodan 

 phylum. 



It remains to bring forward the evidence upon which the 



