80 



BULLETIN 



UNITED STATES NATIONAL MUSEUM. 



length, where a roughened elevation is met. From this point posteriorly the ischia 

 tapers rapidly to the blunt truncated end (fig. 44), which is triangular in cross- 

 section. The height and rugoseness of this elevation on the superior border of the 

 ischium is more pronounced in fully adult specimens. The inferior border presents 

 a thin, sharp edge, except at the transversely expanded 

 distal extremity, which is flattened and has a roughened 

 surface that appears to have been closely applied to the 

 postpubis. In the restoration of the pelvis of Stegosaurus 

 (fig. 42), Marsh 1 has indicated the ischium and postpubis 

 as being in contact along their whole length, but it would 

 appear from the study of specimens in the National Museum 

 collections that there was a longitudinal cleft between them, 

 as in Omosaurus. 



In plate 80, figure 5, Dinosaurs of North America, Marsh 

 shows the distal third of the ischia as meeting on the median 

 line. The shortness of these bones, in conjunction with the 

 great width of the sacrum, appears to make such a union 

 impossible, and in an unpublished plate of the articulated 

 sacrum they are shown only in contact at their ends. Fur- 

 thermore, none of the seven ischia in these collections shows 

 inner surfaces adapted to or even suggestive of such a' carti- 

 laginous symphysis. It is also noted that in the mounted 

 skeleton of S. ungulatus in the Peabody Museum of Yale University the ends of the 

 ischia are not in juxtaposition (pi. 36). 



Nopcsa 2 lays particular stress on the cleft between the pubis and ischium. He 

 says: 



The longitudinal cleft between the pubis and the ischium, which is present in both species of 

 Omosaurus and our Stegosaurus [S. prisms] is a character found in all primitive Ornithopoda; the clos- 

 ing of this cleft observable in 5. ungulatus must, therefore, be regarded as a mark of specialization. 



In view of what is now known of the manner of articulation of these bones, 

 little weight is to be given Nopcsa's observations. 



Measurements of ischia. 



Fig. 44.— Right ischium of 

 Stegosaurus ungulatus 

 Marsh. A nat. size. In- 

 ternal VIEW. a, ANTERIOR 



end; i, articular end for 

 ilium; p, pubic articula- 

 tion; s, symphtsial border. 

 After Marsh. 





No. 4934. 



No. 2111. 





mm. 

 555 

 280 



mm. 

 490 

 262 

 55 









195 







Hind Limb and Foot. 



Femur The femur of Stegosaurus is by far the largest bone in the skeleton. 

 It is remarkably long and slender, with a very straight shaft of nearly uniform 

 width, being somewhat compressed from front to back. The head is not distinct, 



Amer. Journ. Sci., vol. 21. 1881. pi. S, tig. 2. 



2 Geol. Mag., vol. 8, No. 4, p. 151. 



