M, R. Thorpe — John Day Eporeodons. 93 



Aet. yil. — John Day Eporeodons, with Descriptions 

 of New Genera and Species; by Malcolm Ruther- 

 ford Thorpe. 



[Contributions from the Othniel Charles Marsh Publication Fund, Pea- 

 body Museum, Yale University, New Haven, Conn.] 



Table of Contents. 

 Introduction. 

 Description of species. 



Eporeodon occidentalis (Marsh). 



E. leptacanthus leptacanthus (Cope). 



E. leptacanthus pacificus (Cope). 



E. trigonoceplialus trigonoceplialus (Cope). 



E. trigonoceplialus parvus, subsp. nov. 



E. longifrons (Cope). 



E. major (Leidy). 



E. hullatus (Leidy). 



E. condom, sp. nov. 



E. perhullatus, sp. nov. 



Oreodontoides oregonensis, subgen. et sp. nov. 



Paroreodon marshi, gen. et sp. nov. 

 References. 



Introduction. 



In 1875 Marsh founded the genus Eporeodon on a skull 

 collected about 1870 by Eev. Thomas Condon in the John 

 Day basin, Oregon. By some students, this genus may 

 be considered synonymous with Eiicrotaphus Leidy; the 

 present author, however, regards Eucrotaphus as a syno- 

 nym of Agriochoeriis, for reasons to be stated in a subse- 

 quent paper. 



In determining the geologic horizon of the specimens, 

 the same criterion has been employed as that used by the 

 West Coast paleontologists, i. e. specimens showing any 

 green coloration in the matrix should be considered as 

 middle John Day, and those with light colored matrix, 

 grey to buff, as belonging to the upper series. Using 

 this datum, it is found that of 218 specimens in the Marsh 

 Collection at Yale, 184 show unmistakable green colora- 

 tion in the matrix, and 34, grey or buft' colors. In other 

 words, 84 per cent of the specimens of Eporeodon in the 

 John Day basin are found in the middle John Day, and 

 the remainder, 16 per cent, in the upper. The genus 

 Pr ornery CO choerus overlaps downward into the middle 

 John Day in about the same proportion. 



Geologically, the John Day formation is divided into 

 lower, middle, and upper. Paleontologically, the lower 



Am. Jour. Sci. — Fifth Series, Vol. II, No. 8. — August, 1921. 

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