OSTEOLOGY OF THE ARMORED DINOSAURIA. 105 



Type-specimen. — Cat. No. 4934, U. S. N. M. A comparatively complete articu- 

 lated skeleton. The parts preserved are listed below. 



Skull. Two phalanges (proximal row 

 Lower jaws. digits III, IV, left fore foot). 



Atlas. One carpus (left). 



Axis. One radiale (right). 



Twenty-five presacral vertebrae. Three metacarpals (right). 



Three sacral vertebrae. Five ? phalanges (right). 



Twenty-two caudal vertebrae. Two femora. 



Five cervical ribs. One tibia (right). 



Twelve thoracic ribs (right). One fibula (right). 



Thirteen thoracic ribs (left). One astragalus (right). 



Four chevron. One calcaneum (right). 



One scapula (left). Two ilia. 



One coracoid (left). Two ischia. 



Two humeri. Two pubes. 



Two ulnae. Seventeen dermal plates. 



Two radii. One dermal spine. 



Four metacarpals (II, III, IV, V Numerous dermal ossicles, 

 of left fore foot) . 



Collected by Mr. M. P. Felch, 1885-1886. 



Type-locality. — Quarry No. 1, Garden Park, near Canon City, Fremont County, 

 Colorado. 



Horizon. — Morrison, Upper Jurassic. 



The original description, by Marsh, is as follows: 



The skull of Stegosaurus is long and slender, the facial portion being especially produced. Seen 

 from the side, with the lower jaw in position, it is wedge-shaped, with the point found by the premax- 

 illary, which projects well beyond the mandible. The anterior nares are large and situated far in front. 

 The orbit is very large and placed well back. The lower temporal fossa 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 jaws cover the teeth entirely. 



Seen from above, the wedge-shaped form of the skull is still apparent. The only openings visible 

 are the supratemporal fossae. The premaxillary bones are short above, but send back a long process 

 below the narial orifice. The nasal bones are very large and elongate. They are separated in front by 

 the premaxillaries and behind by anterior projections from the frontal bones. The prefrontals are 

 short and externally join the postfrontals. The parietals are small and closely coossified with each 

 other. Viewed from in front the skull and mandible present a nearly quadrate outline [pi. 9, fig. 1] 

 and the mutual relations of the facial bones are well shown. In this view is seen also the predentary 

 bone, a characteristic feature of the mandible in this genus. The lateral aspect of this bone is shown 

 in figure [pi. 5]. The teeth in this genus are entirely confined to the maxdlary 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 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 specimen, with nearly all 

 the dermal armor in place, were found in almost 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 Stegosaurus have been discovered. 



