2 Frof. 0. C. Marsh — Gigantic Ceratopsidce. 



The Skull. 



The skull of Triceratops, the best known genus of the family, has 

 many remarkable features. First of all its size, in the largest 

 individuals, exceeds that of any land-animal, living or extinct, 

 hitherto discovered, and is only surpassed by that of some of the 

 Cetaceans. The skull represented in Plate L, the type of the 

 species, is that of a comparatively young animal, but is about six 

 feet in length. The type of Triceratops horrid us was fully adult, 

 and probably an old individual. The skull, when complete, must 

 have been over eight feet in length. Two other skulls, both nearly 

 perfect, now under examination by the writer, fully equal in bulk 

 the two already described, and other similar specimens from the 

 same horizon maintain equal average dimensions. 



Another striking feature in the skull of this genus is its armature. 

 This consisted of 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 around the margin of the posterior crest. 

 All these had a horny covering of great strength and power. For 

 offence or defence, they formed together an armour for the head as 

 complete as any known. This armature dominated' the skull, and 

 in a great measure determined its form and structure. 



The skull itself is wedge-shaped in form, especially when seen 

 from above. The facial portion is vei*y narrow, and much prolonged 

 in front, as shown in Plate I. Fig. 2. In the frontal region, the 

 skull is massive, and greatly strengthened to support the large and 

 lofty horn-cores, which formed the central feature of the armature. 

 The huge, expanded parietal crest, which overshadowed the back of 

 the skull and neck, was evidently of secondary growth, a practical 

 necessity for the attachment of the powerful ligaments and muscles 

 that supported the head. 



The front part of the skull shows a very high degree of specializa- 

 tion, and the lower jaws have been modified in connection with it. 

 In front of the premaxillaries, there is a large massive bone, not 

 before seen in any vertebrate, which has been called by the writer, 

 the rostral bone (os rostral e). It covers the anterior margins of the 

 premaxillaries, and its sharp inferior edge is continuous with their 

 lower border. This bone is much compressed, and its surface very 

 rugose, showing that it was covered with a strong horny beak. It 

 is a dermal ossification, and corresponds to the pre-dentary bone 

 below. The latter, in this genus, is also sharp and rugose, and like- 

 wise was protected by a strong horny covering. The two together 

 closely resemble the beak of some of the turtles, and as a whole 

 must have formed a most powerful weapon of offence. 



In the skull figured on Plate I. the rostral bone was free, and 

 was not secured. This was also true of the predentary bone, and 

 the nasal horn-core. Hence these parts are represented in outline, 

 taken from another specimen, in which they are present, and in 

 good preservation. 



The premaxillary bones are large, and much compressed trans- 

 versely. Their inner surfaces are flat, and meet each other closely 



