PLATE 3 



UPPER TEETH OF MIOHIPPUS FROM SOUTH DAKOTA AND OREGON. 



All figures natural size. 



Cheyenne River, So. Dak. Upper Oligoeene 1. 



Lower Rosebud, So. Dak. Lower Miocene 



2. 

 3. 

 4. 

 5. 

 6. 

 7. 



Left column. 



Miohippms meteulophus Osborn, type, Am. Mus. 1210 (partly re- 

 versed in drawing). 

 M. brachystylus Osborn, type, Am. Mus. 11860. 

 M. intermedins Osborn and^Wortman, type, Am. Mus. 1196. 

 M. gidleyi Osborn, type, Am. Mus. 1192. 



M. validus Osborn, type, Am. Mus.' 1218 (partly reversed in drawing). 

 M. equinanus Osborn, type, Am. Mus. 12912. 



M. gemmarosce, type, Am. Mus. 13808 (partly reversed in drawing). 



Middle John Day, Ore. Upper Oligoeene 



John Dav River, Ore. 



Lower Miocene 



8. 



9. 

 10. 

 13. 

 14. 

 12. 



Cheyenne River, So. Dak. Upper Oligoeene 11. 

 John Day River, Ore. Lower Miocene 15. 



Right column. 

 M. qudrtus Osborn, type, Am. Mus. 7267. 

 M. brachylophus Cope, referred specimen, Am. Mus. 7262. 

 M. equiceps Cope, type, Am. Mus. 7261. 

 M. primus Osborn, type, Am. Mus. 7291 (reversed in drawing). 

 M. annectens Marsh, cotype or referred specimen, Yale Mus. 12230. 

 M. rondoni Leidy, type, Acad. Nat. Sci. Phila. (drawn from Leidy's 

 figure). 



M. crassicuspis Osborn, type, Am. Mus. 683 (reversed in drawing). 

 M. annectens Marsh, type, Yale Mus. 11275. 



The upper teeth included within the Miohippus stage extend from the species M. meteulophus of the Leptauchenia zone 

 to those of M. gemmarosae of the Promerycochoerus zone of the Lower Rosebud. They are distinguished by variations 

 in size, by varying degrees of development of the hypostyle, which is rudimentary in M. meteulophus, an elongate loop in 

 M. brachystylus, a triangular fold in M. intermedius, M. validus, and M. gemmarosae, and by the progressive development 

 of the protoconule and metaconule. 



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