1902.] Matt/iezv, A Horned Rodent from Colorado Miocene. 299 



Dimensions . 



Lower jaw, diameter of enlarged molar, anteroposterior(grmd- 



ing surface) 9 mm . 



Lower jaw, diameter of enlarged molar, transverse (grinding 

 surface) 5 



Upper jaw, diam. of enlarged molar, anteroposterior (grind- 

 ing surface) 9 



Upper jaw, diam. of enlarged molar, transverse (grinding sur- 

 face) 5.8 



Ceratogaulus rhinocerus, n. sp. 



Generic characters: Nasals bearing a large pair of horn-like 

 processes, closely twinned. Specific characters: Size some- 

 what larger than that of M. IcBvis, less than that of M. mono- 

 don. Enamel lakes of lower molar simpler, seven in number, 

 arranged in three rows, less regular than those in M. monodon 

 or M. IcBvis. Alveoli of last two molars of subequal size. Ex- 

 ternal side of upper grinder flat, internal strongly convex. 

 Second upper grinder larger than third. Muzzle broader 

 than in AI. Icevis, postorbital processes shorter and more 

 posterior. 



Dimensions of the Enlarged Grinders. / p-f 



Upper. Lower. \ Ti\fc-^? 'I 1 



Anteroposterior diameter . 8.7 mm. 9.7 mm. \V' ' \j\ I 



Transverse " .6.5 5.5 ^-X__J/ 



Mylagaulus paniensis, n. sp. / 



A small and simple species indicated by |^^,/ 



half a lower jaw and a few fragments. M.. 



There are five enamel lakes, of which the /^\ 



three interior ones are arranged in a row as Jf^ 



in M. ballensis; and external to these are a fwj'''-'^ 



large and a small lake, the latter correspond- ^^ 



ing to the fourth lake of ballensis. The /««'/>««>, pan ol'^uwer 



tooth is worn well down, while that of L^;p Fork^^(Pawnei 



7 77 • j_ -L. X" 1 Creek Beds), Colorado. 



ballensts appears to be a comparatively 



young individual, so that the less number of lakes in Mr, 



Riggs's species can hardly be due to greater age; and on 



