-±14 0. C. Marsh — Skull and Armor of Stegosaurus. 



The Skull. 



The skul] of Stegosaurus is long and slender, the facial por- 

 tion being especially produced. Seen from the side, with the 

 lower jaw in position, it is wedge-shaped, with the point 

 formed by the premaxillary, which projects well beyond the 

 mandible, as shown in figure 1, Plate VI. The anterior nares 

 (a) are large, and situated far in front. The orbit (b) is very 

 large, and placed well back. The lower temporal fossa (c) is 

 somewhat smaller. All these openings are oval in outline, and 

 are on a line nearly parallel with the top of the skull. In this 

 view, the lower jaw covers the teeth entirely. 



Seen from above, as shown in figure 3, Plate YI, the wedge- 

 shaped form of the skull is still apparent: The only openings 

 visible are the supra-temporal fossse (e). The premaxillary 

 bones (pm) are short above, but send back a long process below 

 the narial orifice. The nasal bones (n) are very large, and 

 elongate. They are separated in front by the premaxillaries, 

 and behind, by anterior projections from the frontal bones. 

 The prefrontals (jpf) are large, and are placed between the 

 nasals and the prominent, rugose supra- orbitals (so). The 

 frontals are short, and externally join the postfrontals (fp)- 

 The parietals are small, and closely coossified with each other. 



Viewed from in front, the skull and mandible present a nearly 

 quadrate outline (Plate VI, figure 2), and the mutual relations 

 of the facial bones are well shown. In this view is seen, also, 

 the predentary bone (pd), a characteristic feature of the mandi- 

 ble in this genus. The lateral aspect of this bone in shown in 

 figure 1. 



The teeth in this genus are entirely confined to the maxillary 

 and dentary bones, and are not visible in any of the figures here 

 given. They are small, with compressed, fluted crowns, which 

 are separated from the roots by a more or less distinct neck. 

 The premaxillary and the predentary bones are edentulous. 



The present skull belongs to the type specimen of a new 

 and very distinct species, which may be called Stegosaurus 

 stenops. The skull and nearly complete skeleton of this speci- 

 men, with nearly all the dermal armor in place, were found 

 almost in the position in which the animal died. 



This animal was much smaller than those representing the 

 other species of this genus. Its remains were found by Mr. 

 M. P. Felch, in the Atlantosaurus beds of the Upper Jurassic, 

 in southern Colorado. In this geological horizon, all the 

 known American forms of Stegosauria have been discovered. 



