THE MAMMALIA OF THE DEEP EIVER BEDS. 127 



B. Lower Jaw. The incisors are smaller than in JSporeodon and have chisel- 

 shaped crowns, with an internal cingulum upon the second and third ; all three are of 

 nearly equal size and are quite strongly procumbent. The canine is larger than the 

 incisors, to which series it functionally belongs, and is, like them, quite procumbent. 



The first premolar has the caniniform shape and function characteristic of all the 

 genera of the family except Pltliecistes ; there is a very marked difference in the size 

 and shape of this tooth in the various specimens, a difference which is doubtless sex- 

 ual. In those skulls which are supposed to be of females, pTI is much lower and 

 smaller, and in shape less completely caniniform than in the males. The other pre- 

 molars in all the available specimens are so abraded that the details of their construc- 

 tion cannot well be made out ; they are longer in the antero-posterior direction than 

 those of JEporeodon, and M is implanted by two well-separated fangs. In p. 4, which 

 is less rapidly worn down than the other premolars, there are two deep internal val- 

 leys, one in front of and the other behind the deuteroconid ; the posterior valley be- 

 comes, on abrasion, an isolated fossette. 



The molars are much more like those of JEporeodon than those of Merychyus in 

 the general shape of their broad, low crowns; but the valleys are narrow and soon 

 disappear on wear, and the inner lobes are somewhat more flattened than in the John 

 Day genus. 



Measurements. 



MALE. FEMALE. 



M. M. 



Upper molar-premolar series, length 103 .101 



Upper premolar series, length 048 .048 



Upper canine, antero-posterior diameter (fang) 009 .008 



Upper canine, transverse diameter (fang) 012 .010 



Upper first premolar, length 010 .011 



Upper second premolar, length 013 .014 



Upper third premolar, length 013 .013 



Upper fourth premolar, length 012 .012 



Upper fourth premolar, width .014 



Upper molar series, length 055 .053 



Upper first molar, length : 015 .012 



Upper first molar, width -015 



Upper second molar, length 018 .016 



Upper second molar, width -021 



Upper third molar, length 025 .024 



Upper third molar, width -025 



Lower molar-premolar series, length 107 .109 



Lower premolar series, length 048 .046 



Lower first premolar, length 010 .008 



Lower first premolar, width 009 .006 



A. P. S. — VOL. XVIII. Q. 



