12 Prof. O. C. Marsh—On Stegosaurus. 
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 Fig. 3, Plate I., the wedge-shaped 
form of the skull is still apparent. The only openings visible are 
the supra-temporal fosse (e). The premaxillary bones (pm) are 
short above, but send back a long process below the narial orifice. 
The nasal bones (x) are very large, and elongate. They are 
separated in front by the premaxillaries, and behind, by anterior 
projections from the frontal bones. The prefrontals (pf) are large, 
and are placed between the nasals and the prominent, rugose supra- 
orbitals (so). The frontals are short, and externally join the post- 
frontals (fp). The parietals are small, and closely codssified with 
each other. 
Viewed from in front, the skull and mandible present a nearly 
quadrate outline (Pl. I. Fig. 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 mandible in this genus. 
The lateral aspect of this bone is shown in Fig. 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 very distinct 
species, which the writer has called Stegosaurus stenops. The skull 
and nearly complete skeleton of this specimen, with nearly all the 
dermal armour 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 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. 
Tue Dermat Armour. 
The osseous dermal covering of Stegosaurus was first described 
by the writer from specimens found associated with several skeletons, 
but not in place, and hence the position of the various parts was a 
matter of considerable doubt. Subsequent discoveries have shown 
the general arrangement of the plates, spines, and ossicles, and it is 
now evident that, while all the group were apparently well pro- 
tected by offensive and defensive armour, the various species, and 
perhaps the sexes, differed more or less in the form, size, and number 
of portions of their dermal covering. This was especially true of 
the spines, which are quite characteristic in some members of the 
group, if not in all. 
The skull was evidently covered above with a comparatively soft 
integument. The throat and neck below were well protected by 
small, rounded and flattened ossicles having a regular arrangement 
in the thick skin. One of these ossicles is shown in Woodcut Fig. 1. 
