260 Annals of the Carnegie Museum. 



Aphelops ceratorhinus Douglass. 1 

 (Plate LXIV.) 



The type of Aphelops ceratorhinus is No. 857, Carnegie Museum 

 Catalogue of Vertebrate Fossils. This specimen was not all acces- 

 sible or fully prepared for study when the first description was made. 

 Fragments of the skull were originally found in a cattle-path on a 

 steep bluff on the east side of the Lower Madison Valley in Montana. 

 By digging into the sand, portions of a much broken skull and a 

 nearly complete mandible were found. A good portion of one side 

 of the skull has been put together, but the upper posterior portion is 

 still wanting. Fragments of vertebrae and limb-bones were found 

 weathered out just below where the skull and mandible were obtained. 

 From the same beds as the type are other portions of the skulls, 

 which, judging by the forms of the nasals and the 

 basal portions of the skulls belong to the same or 

 nearly related species. These enable us to get the 

 approximate proportions of the missing parts of the 

 cranium of Aphelops ceratorhinus and to make the 

 restoration of the skull which is given in Plate LXIV. 

 Principal Distinguishing Characters. — Size large ; 

 skull long (dolichocephalic) ; nasals long and 

 slender, with small terminal horn-rugosities; exter- 

 nal auricular opening closed below ; post-tympanic 

 neum of type of ,. , . . ,., 



/r expanding outward in wing-like processes; parocci- 



kinus 1 pitals concave behind and in front, separated from 



occipital condyles by a concave area ; cheek teeth 

 brachyodont with cingula on interior portions of premolars ; P^ to M^ 

 with crotchets ; mandible long and comparatively shallow, but thick 

 and heavy ; ascending ramus only moderately high, angle rounded, 

 alveoli for canines large. 



Judging from the posterior portion of the skull of another individual 

 (No. 854, see Fig. 3), which is smaller, the occiput was low and nar- 

 rowed upward. The nasals turned downward slightly at the tips just 

 anterior to the nasal rugosities. The borders of the nasals, beginning 

 at the rugosities, expand and have a decidedly downward trend for 

 more than one half of the distance backward. On the posterior half 



1 " New Vertebrates from the Montana Tertiary," Annals of the Carnegie Mu- 

 seum, Vol. II, No. 2, 1903, p. 195. 



Fig. 2. Calca- 



