852 THE JOHN DAY FAUNA. 



HESPEROMYS Waterhouse. 



This recent genus had a representative in the John Day Miocene in 

 North America, so far as the characters of" the skull and dentition may be 

 considered to be conclusive in evidence. It is not very probable that the 

 indications thus obtained will be invalidated by other portions of the 

 skeleton. 



The molars are |, and the crowns support alternating tubercles sepa- 

 rated by shallow open transverse valleys. These are, one on the inner 

 and two on the outer sides of the superior series, and one on the outer and 

 two on the inner side of the inferior. In the recent species, {H. leucopus) 

 there are two inflections on the inner side of the tirst molar, but in the spe- 

 cies here described that tooth is constricted at the position of the anterior 

 internal loop, and does not regain its width, but continues narrowed to the 

 anterior extremity. Tlie infraorbital foramen is rather large. 



It is probable that there is a second species of this genus in the Loup 

 Fork beds besides the H. loxodon Cope. 



Hesperomys nematodon Cope. 



Paleontological Bulletin No. 31, p. 1, Dec. 24, 1879. Proceedings American Philosoph. Soc, 1879-'80,. 



p. 370. 



Plate LXVI; fig. 33. . 



This rat is represented by a beautiful skull, discovered by Prof. Thomas 

 Condon, of Eugene City, and by several jaws and other fragments subse- 

 quently found by Mr. Wortman. 



The frontal region is not contracted as in JEumi/s clegans and Fiber 

 zibethicus, but the superciliary ridges are well separated from each other, as 

 in Hesperomys americanus. The frontal and posterior nasal regions are 

 slightly concave in transverse section. The molars display tubercles on 

 one side and crescents on the other, the former being external in the supe- 

 rior series. The first superior molar has an additional tubercle at its anterior 

 extremity. The incisors have a transverse anterior face, which is divided by 

 several delicate ridges. 



Length of superior molar series, .0065; length of first superior molar, 

 .0028; interorbital width, .0042 Length of inferior molar series (specimen 



