DINOSAURIA. 213 



of Colorado and Wyoming, where nearly complete skeletons have been 

 found. The typical species, S. ungulatus, probably attained a length of 

 about nine metres. 



Towards the close of the Mesozoic period, when the Dino- 

 saurs gradually become extinct, a remarkable group of gigantic 

 horned animals appears, supposed to be a highly specialized 

 branch of the tribe to which the armoured Stegosauria belong. 

 Unsatisfactory fragments of these reptiles from the Upper 

 Cretaceous, both of Austria and North America, have received 

 many names (e.g., Struthiosaurus, Agathaumas, Polyonax, and 

 Monoclonius) ; but the only important specimens hitherto dis- 

 covered are those from the Laramie Formation of Wyoming, 

 U.S.A., termed Ceratops, Triceratops, and Sterrholophns, the 

 first two thus named in allusion to the great horns of which 

 one pair is placed above the eyes. 



Fio. 132. 



Triceratops prorsus ; restoration of skeleton by 0. C. Marsh, one-eightieth nat. 

 size. Cretaceous ; Wyoming. 



Triceratops (figs. 132, 133). The greater part of the skeleton of this 

 genus is known, and indicates an animal of robust proportions which 

 would be quadrupedal in gait. All the bones are solid. The skull of 

 the largest individuals exceeds in size that of any land-animal hitherto 

 discovered, and is only surpassed by that of some of the modern Ceta- 

 ceans. It is chiefly remarkable for its armature (fig. 133). There is a 

 sharp cutting beak in front, a strong horn on the nose, a pair of very large 

 pointed horns on the top of the head, and a row of sharp projections 

 round the margin of the posterior crest all these doubtless encased in 

 a layer of horny tissue. The skull itself is wedge-shaped in form, and 

 very narrow in the facial portion. The upper toothless beak is formed 

 by the premaxillae, with the addition of a median "rostral" bone in 



