THE MAMMALIA OF THE UnSTTA FOHINrATION. 503 



the Xiphodoiitnla; on account of the presence of the fifth cusp in the anterior half of 

 the upper molars. This airangement is, however, quite untenable, as this unpaired 

 cusp is common to the great majority of the selenodonts and even the bunodonts of 

 the Eocene. On the other hand, the peculiar structure of the premolars in Xipho- 

 (lon, the caniniform premolar of Protoreodon, and the entirely divergent structure 

 of the feet in the two genera, show that their relationship to each other can only be 

 a I'emote one, and that any association of thoui in a single family must be arbitrary. 

 This is especially the case when we consider the obviously close relationship between 

 the Oreodont idee ami Protoreodon, which is recognized in Cope's scheme {I. c, p. 387). 

 K" tiie presence of the fifth cusp be looked upon as a family character, then it will be 

 necessary to form a new ftimily, the Protoreodontidce, for the reception of this genus. 

 But this seems to be unnecessary, and a more natural method would be to regard the 

 Uinta type as forming a subfamily of the Oreodontulce, characterized by the five-lobed 

 up2)er molars, and in other respects combining the features of the Miocene subfami- 

 lies, the Oreodonthue and the Agr/ochain'ni£. This last fact is of particular import- 

 ance, as it proves the connection between AfjriocJioerus and the true oreodonts, and 

 shows that Cope's reference {I. c, p. 388) of this genus to the Diclwdotdidiv, on account 

 of the complication of the last premolars, does not represent the natural arrangement. 

 "Whether we adopt Leidy's view, that Agriochcei-us is the type of a distinct family, or 

 with Gill regard it as representing a subfamily of the Oreodontulce, is a matter of 

 comparatively little importance ; the essential fact being the close genetic connection 

 of the two. 



List of Papers Quoted. 



E. D. Cope.— I. On the Vertebrata of the Wind River Eocene Beds of Wyoming. BuUutin U. S. Geological and Geo- 

 graphical Survi-y of the Territories, Vol. VI. No. 1, pp. 183-202. 



2. The Meso/oic and Ctenozoic Realms of the Interior of North America. Amcriciiii NatunUi^l. Vol. XXI. 



pp. 445-462. 



3. The Verlehmla of the Tertiary Formations of the West. Report of the U. 9. Geological and Geographical 



Survey ol' the Territories, Vol. HI, Pt. I, Washington, 1884. 



4. Synopais of the Species of Oreodontida;. Proceedings of the American Philosophical Society, Vol. .XXI. 



pp. 5()3-.'"j72. 



5. The Classification and Phylogcny of the Artiodaclyla. Ibid., IS.ST, pp. 377-JOO. 



Clarence King.—fi. U. 8. Geological Exploration of the Fortieth Parallel. Vol. I, Systematic Geology, Wash- 

 ington, 1878. 



Joteph Leidy. — 7. The Extinct Mammalian Fauna nf Dakota and Nebraska. .Iourn;il of the ,\c.iilemy of Natural 

 Sciences, Philadelphia. 1800. 



0. C. U'lrth. — H. Notice of New Tertiary Mammals. American Journal of Science and Arts, 3d Ser., Vol. IX, pp. 

 230-250. 

 !i. Introduction and Succession of Verlchrate Life in America. Ibid., Vol. XIV, p. 337. 



