M. S. Lull — Stegosauriis xmgidatus Marsh. 377 



are present, and, in every respect, the older animal differs only 

 in being of a more generalized character. On the other hand, 

 0. armatus of Owen, from the Kimmeridgian, though nearer 

 Stegoscmrus in time, is less like it than is its predecessor in the 

 rocks. 0. arviatus would seem, therefore, to belong to a differ- 

 ent phylum, in many i-espects more conservative than the true 

 stegosaurs. 



That Stegosaurus belonged to the predentate dinosaurs and 

 to tlie armored Stegosauria, is certain. It is not, however, in 

 the direct line of descent, but rather an over-specialized side 

 branch, which was apparently totally blotted out after Morrison 

 time, despite the fact that most of its associates, except the Sau- 

 ropoda, lived on. 



The spinescent character of Stegosaurus is of course indica- 

 tive of racial senility, but the modernizing of the flora and the 

 restriction, doubtless, of the special food plant to which the 

 feeble mouth armament was adapted, may have been the 

 immediate cause of extinction. 



The skeleton has been mounted under my direction by Head 

 Preparator Hugh Gibb, assisted by W. S. Benton, and is a mon- 

 ument to their skill and industry. 



Am. Jour. Sci.— Fourth Series, Vol. XXX, No. 180.— December, 1910. 

 35 



