168 0. C. Marsh — The gigantic Ceratopsidce, 



The fossils associated with the Oeratopsidw are mainly- 

 Dinosaurs, representing two or three orders, and several 

 families. Plesiosaurs. crocodiles and turtles of Cretaceous 

 types, and many smaller reptiles, have left their remains in 

 the same deposits. Numerous small mammals, also of ancient 

 types, a few birds, and many fishes, are likewise entombed in 

 this formation. Invertebrate fossils and plants are not un- 

 common in the same horizon. 



The Skull. 



The skull of Tricerafops. the best known genus of the 

 family, has many remarkable features. First of all, its size r 

 in the largest individuals, exceeds that of any land animal 

 hitherto discovered, living or extinct, and is only surpassed by 

 that of some of the Cetaceans. The skull represented natural 

 size in two of the diagrams was that of a comparatively young 

 animal, but is about six feet in length. The type specimen of 

 Trice rral 'op ■$ karridus was an old individual, and the head, 

 when complete, must have been seven or eight feet in length. 

 Two other skulls, nearly perfect, represented by life-size 

 sketches, and several others from the same horizon, have 

 almost equal dimensions.* 



Another striking feature of the skull is its armature. This 

 consisted of a sharp, eutting 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 homy covering of 

 great strength and power. For offense and defense, they formed 

 together an armor for the head as complete as any known. 

 This armature dominated the skull, and in a great measure, 

 determined its form and structure. In some forms, the arma- 

 ture extended over portions of the body. 



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

 seen from above. The facial portion is very narrow, and much 

 prolonged in front. 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, posterior crest, which overshadowed the back of 

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

 practical necessity for the attachment of the powerful liga- 

 ments and muscles that supported the head (Plate I. figures 

 1-4 . 



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

 specialization, and the lower jaws have been modified in 



* The large diagrams shown when this paper was read are most of them 

 tilted by reduced figures in the accompanying Plates, I-X. 



