216 DINOSAURS OF NORTH AMERICA. 



originally with the supratemporal fossse. Another pair of still smaller 

 foramina may be seen in the same skull, close to the median line, and 

 separated from each other by the anterior projection of the parietal. 

 A deep groove leads forward to each of these foramina, along the 

 suture between the parietal and the postfroutal. The position and 

 direction of these perforations suggest that they may correspond to the 

 foramen seen iu Triceratops, and shown on PI. LX, fig. 3, ./■. The same 

 foramen is shown above in fig. 54. 



The extreme lightness and great expanse of the posterior crest in 

 Torosaurus make it probable that it was encased in the integuments of 

 the head, and that no part of it was free. The outer borders of both 

 the parietal and the squamosals show no marginal ossifications, as in 

 the other known genera of the group, but the presence of a large, 

 separate, epijugal bone in one specimen suggests that epoccipitals may 

 yet be found. 



The open perforations in the parietal, which have suggested the name 

 Torosaurus, readily separate this genus from all the gigantic species 

 hitherto known in the Oeratopsidae, but may perhaps be found in some 

 of the smaller and less specialized forms, from lower horizons of the 

 same formation. 



CEEATOPS. 



The genus Ceratops so far as at present known is represented by indi- 

 viduals of smaller size than those of Triceratops, and in some instances, 

 at least, of quite different proportions. The type specimen is shown 

 in PL LXIII. A third genus, Sterrholophus, can be readily distin- 

 guished from the other two by the parietal crest, which had its entire 

 posterior surface covered with the ligaments and muscles supporting 

 the head. In Ceratops and Triceratops a wide margin of this surface 

 was free, and protected by a thick, horny covering. There is some 

 evidence that still other forms, quite distinct, left their remains in 

 essentially the same horizon, but their true relation to the above genera 

 can not be settled without further discoveries. 



STERRHOLOPHUS. 



With the successive changes in the parietal in the Ceratopsida j , there 

 were corresponding variations in the squamosals, and these bones also 

 will serve to distinguish the principal genera from one another. In PI. 

 LXIII the squamosals of three genera of this group are shown, and the 

 wide difference between them, when seen from the inside, is especially 

 noticeable. In fig. i of this plate, the long, slender, right squamosal 

 of Torosaurus, with its smooth outer border, is well represented. In 

 fig. 5 is seen the same bone of Sterrholophus, with a serrate outer 

 margin and smooth inner surface, also shown in fig. 1 of PI. LX. Xext, 

 iu fig. is the small, short squamosal of Ceratops, nearly bisected by its 

 deep quadrate groove. The free sculptured border of both the parietal 

 and squamosals of Triceratops is clearly shown in PI. LX, fig. 4, where 

 the contrast with the corresponding parts in fig. 2 is noteworthy. 



