MAMMALIA. 



Dinoceras (figs. 169, 170). The skull in this genus is long and narrow, 

 with an elevated, more or less quadrangular occiput, and a much-produced 

 facial region. The basicranial axis is straight. The top of the skull 

 supports three transverse pairs of smooth bony prominences, which form 

 its most conspicuous feature and are alluded to in the generic name. 

 These prominences are not separate ossifications, but merely elevations 

 upon the nasal, maxillary, and parietal bones respectively, and the smooth- 

 ness of their surface shows that they cannot have been encased in ordinary 



ill B 



FIG. 169. 



Dinoceras mirabile; outline of upper aspect of cranium showing also size and 

 form of brain-cavity (A), drawing of left manus (B), and drawing of left pes 

 (c), the first being one-eighth, the others one-fifth nat. size. M. Eocene 

 (Bridger Formation) ; Wyoming. (After Marsh.) 



horn. They increase in size backwards, the parietal prominences being 

 relatively very large, and raised on a conspicuous crest which extends from 

 near the orbits entirely round the lateral and posterior margins of the 

 cranium. The cranial roof is thus much thickened, but air-cavities are 

 few and rare. The orbit is large and confluent with the temporal fossa, 

 while there is not even a postorbital prominence of the frontal region. 

 The sutures between the various elements can usually be observed in 



