THE 



AMERICAN JOURNAL OF SCIENCE 



[FIFTH SERIES.] 



Aet. XIY. — John Day Pr ornery co cheer iy with Descrip- 

 tions of Five Neiv Species and One Neiv Subgenus; by 

 Malcolm Rutheefokd Thorpe. 



[Contributions from the Othniel Charles Marsh Publication Fund, Peabody 

 Museum, Yale University, New Haven, Conn.] 



Table of Contents. 

 Introduction. 

 Geological sketch. 

 Geographic distribution of species. 

 Description of species. 



Promerycochoerus suyerhus (Leidy). P. inflatus, sp. nov. 



P. chelydra (Cope). P. marslii, sp. nov. 



P. macrostegus (Cope). P. micro cephalus, sp. nov. 



P. leidyi (Bettany). Desmatochoerus curvidens, subgen. 



P. lulU, sp. nov. et sp. nov. 



P. latidens, sp. nov. 

 Synopsis of John Day species. 



Introduction. 



One of the most remarkable features of the specimens 

 of the John Day genus Promerycochoerus in the Marsh 

 Collection is the unusual variation shown in the tooth 

 structure. Styles are developed on the molar teeth, both 

 from the cingulum and from the cone itself, with such 

 frequency that they become of no value for specific deter- 

 minations. The metastyles of M^ exhibit great variation 

 in size and in robustness, as well as in the degree of 

 inward rotation. Likewise, there is variation in the pro- 

 portions of size between the superior molars in different 

 individuals. It is interesting to note in this connection 

 that the paratype of Merycochoerus proprius Leidyi has 



^Joseph Leidy, Jour. Acad. Nat. Sci., Philadelphia (2), 7, 110, 380, pi. 10, 

 fig. 5, 1869. This paratype is No. 445, U. S. National Museum, and was- 

 found near Ft. Laramie, Wyo. 



Am. Jour. Sci. — Fifth Series, Vol. I, No. 3.— March, 1921. 

 15 



