Cope.] *b [August 15, 



not commit himself as to this point, but allows the development of the 

 two types of dentition to appear to have been cotemporary and from some 

 common origin. He then derives from such a common point of departure 

 first, the Hyopotamidse, which first appear in the Eocene, and second, the 

 ancestors of the Anoplotheriidse. From the Hyopotamidae he derives all 

 the modern Selenodonta, exclusive of the Camelidae. The latter group 

 he omits from his table, doubtless because his information on the subject 

 was insufficient. The main line of origin of the Selenodonta is divided 

 early in Miocene time, the genus Gelocus giving origin to the Pecora, and 

 the genus Hygemoschus to the Tragulina. 



In describing the characters of the genus Poebrotherium for the first 

 time, I remarked as follows :* "The present genus is a more generalized 

 type than Gelocus, and in its distinct trapezoid and distinct metacarpals 

 represents an early stage in the developmental history of that genus. It 

 also presents affinity to an earlier type than the Tragulidse which some- 

 times have the divided metacarpals, but the trapezoides and magnum co- 

 ossified. In fact Poebrotherium as direct ancestor of the camels, indicates 

 that the existing Ruminantia were derived from three lines represented by 

 the genera Gelocus for the typical forms, Poebrotherium for the camels 

 and Hysemoschus for the Tragulidse." 



These views being then established on sufficient evidence, it remains to 

 make such additions as the facts cited in the present paper indicate. First 

 in importance comes the place in the phylogeny of the Selenodonta, of 

 the Oreodontidse. The peculiar inward extension of the unciform bone 

 already ascribed to them, characterizes also among extinct forms the genus 

 Leptomeryx, and probably Hypertragulus. Among recent ruminants it 

 is only seen in the Tragulidse. f If we arrange these types in serial order 

 we find the modifications of form to be generally identical with those of 

 the other ruminant lines, in the coossification of the bones of the legs and 

 feet. This series may then be regarded as phylogenetic. The peculiar 

 structure of the carpus of the Oreoclontidae, puts them out of the question 

 as ancestors of any type of existing ruminants other than the Tragulina. 

 Whether they themselves can be traced to a five-lobed, or to a four-lobed 

 bunodont ancestor, remains an undecided question. It is not, however, 

 probable that a five-lobed form has been intercalated in a series, both of 

 whose extremities are four-lobed. If this be true, the Oreodontidee must 

 be regarded as an ancestral type of Selenodonta, coequal with the Hyopo- 

 tamidse, and it may well be questioned whether the latter can have been 

 ancestors of the existing Ruminantia, whose molars are four-lobed. 



So the present investigation does not disclose the ancestral stock of the 

 Pecora. In North America we have not progressed further in the solu- 

 tion of this question than I reached in 1877,:): after a study of the genera 



* Bulletin U. S. Geol. Survey Terrs. Vol. 1, No. 1, p. 26, Jan., 1874. 



t Among Perissodactyles it occurs in Triplopus, Tapirus and the Rhinoceron- 

 tidae. 

 % Proceedings Amer. Philos. Soc. p. 223. 



