1902.] Matthew, A Hortied Rodent from Colorado Miocene. 293 



the teeth being sHghtly less advanced. The distinctions, 

 therefore, cannot be due to age. The horn-Uke processes 

 might be sexual, although I can find no parallel among the 

 rodents for such a wide divergence between male and female ; 

 but the marked distinctions in the teeth and other characters 

 are not likely to be sexual, although in themselves they are 

 not of generic importance. 



The height of the horn-cores is about one-fifth the length 

 of the skull, their length a little more, and their conjoined 

 width about one-fourth the skull-length. The longer axis of 

 each process is diagonal, posteroexternal and anterointernal ; 

 the conjoined process is subtrigonal, the angles posteroexter- 

 nal and anterior. 



A character so marked as this would seem a good basis for a 

 separate genus. Nevertheless, the resemblance to the skull 

 of Mylagauhis obtained in 1898 is considerable in most char- 

 acters, except in the horn-cores, the position of the postor- 

 bital processes, and the pattern of the enlarged grinding teeth. 



The occiput is extraordinarily wide and low, its width 

 equalling the entire length of the skull. The postorbital 

 crests do not unite behind; the top of the skull is flat trans- 

 versely, concave anteroposteriorly, and the occipital surface 

 slopes 30° forward from the condyles to the top of the crest. 

 The zygomatic arches are stout, deepest in front, somewhat 

 wider than the occiput, both postorbital processes (on the 

 frontal and jugal) moderately strong. In both upper and 

 lower jaws the alveoli of two smaller molars are preserved, 

 but no clear indication of a third, behind the enlarged tooth. 



Measurements. 



Length of skull (condyle estimated) 68 mm. 



Width across arches 64 



" of occiput 65 



Height of horn-core 13 



Length " " 17 



Conjoined width of horn-cores 19 



Width across postorbital processes of frontals 32 



Width across postorbital constriction 18 



Least depth of zygomatic arch beneath orbit 9 



