A NEW DINOSAUR, STP^GOSAURUS MARSHl, FROM THE 

 LOWER CRETACEOUS OF SOUTH DAKOTA. 



By Frederic A. Lucas, 



Curator, Divisioii of Coiiipnrative Anatomy, in charge, of Section of Vertebrate Fossils. 



The name Stec/osaurus marshi is proposed for a new species of 

 Stcg-osaur represented by a number of plates, spines, and portions 

 of the nuchal and gular armature, as well as by some vertebra and 

 bones of the limbs, obtained by Mr, N. H. Darton in South Dakota 

 from beds considered liy him to be of Lower Cretaceous age. 



This material, which is in the U. S. National Museum and is the type 

 of the species, is numbered 4752 in the catalogue of fossil vertebrates. 

 It was found associated with remains of another dinosaur of moderate 

 size, probably related to Camptosaurus. The species is characterized 

 by the general massive appearance of the plates and spines, the com- 

 paratively large extent of their basal surfaces, their abrupt taper 

 and sharp edges. In these respects they are quite different from the 

 corresponding portions of any other Stegosaur yet discovered, and 

 coming as they do from the highest horizon in which remains of 

 Stegosaurs have been found thej^ may be considered as representing 

 the latest developments in the dermal armature of this remarkable 

 group of dinosaurs. 



A dermal spine, found by Mr. J. B. Hatcher, in conjunction with 

 remains of Triceratops. and regarded at the time as belonging to 

 that genus, may very likely have come from the species under 

 consideration. 



A spine, shown on Plate XXIII, presumably from near the posterior 

 end of the caudal series, has a long and comparatively wide basal 

 portion and then tapers rapidly to a spike-like form. 



A plate, shown on Plate XXIV, apparently from the caudal series, 

 somewhat in advance of the spine just described, is trianguhir in 

 section, slightl}- rounded on one surface, while on the other it tapers 

 abruptl}^ from the base with a concave curve. 



Proceedings U. S. National Museum, Vol. XXIII— No. 1224. 



591 



