II. F. shorn — Mammalia in North America. 463 



molars. As the origin of the rhinoceroses still remains a mys- 

 tery, so their later evolution needs clearing up. The Ameri- 

 can series suddenly terminate in the huge, hornless forms of 

 the upper Miocene. I find there is still no unanimity of 

 opinion as to the phyletic relationships of the Miocene, Plio- 

 cene and existing species of Europe. 



Succession of the Art lo dactyls. 



The Eocene Artiodactyl phylogeny is still far behind that of 

 the perissodactyls, but the Miocene and Pliocene succession 

 has been worked up with great success and clearness by Cope 

 and Scott. The latter says in a recent paper: "All the great 

 groups of Artiodactyla are seen to arise independently from 

 the Buno-Selenodonta which forms as it were a lake, from 

 which several streams, flowing partly in parallel partly in 

 divergent directions, are derived." 



The Elotheriidse appear in Parahyus of the Bridger and 

 Achsenodon of the Washakie, and terminate in the middle 

 Miocene in the gigantic Elotherium ramosum, an animal with 

 a skull three feet long, both the jaws and skull being armed 

 with long branching processes. The true bunodont pigs and 

 peccaries have not yet been found lower than the White River. 



Scott has traced the Oreodons back to Protoreodon of the 

 top of. the Eocene. The aberrant Agriochceridse, he believes, 

 were doubtfully connected with the true Oreodons by a lower 

 Eocene stem form. The true Oreodons, which existed in great 

 herds in the lower Miocene, have been divided by Cope and 

 Scott into three parallel lines extending into the Loup Fork, 

 namely, the large Merycochcerus, the medium-sized Merychyus 

 and the small, highly-specialized Pithecistes. 



The Tragulines are represented by Leptomeryx, Hyper- 

 tragulus and Hypisodus. Leptomeryx is believed to be a side 

 member of the main family. 



Here I may speak of the recent discovery of the characters of 

 the ProtoceratidsB, a new family with a remarkable ensemble 

 of characters. In 1891 Marsh described the female skull of 

 Protoceras with a small pair of parietal protuberances. The 

 male skull was found by the American Museum party of 

 1892. It is armed not only by upper canine tusks, but 

 by four pairs of cranial protuberances, two of which might 

 be dignified by the name of osseous horns; it thus presents 

 the armature of an Uintatherium upon a small scale. Besides 

 parietal and two pairs of frontal protuberances, there are a 

 pair of most exceptional maxillary plates. The fore foot is 

 like that of Tragulus, while the hind foot is didactyl like the 

 deer. We can at present form no idea of its affinities. 



