156 THE CERATOPSIA. 



characteristic feature in this genus is the dermal armor, which appears to have been more complete than in any of the 

 American forms hitherto found. This armor covered the sides closely and was supported by the ribs, which were especially 

 strengthened to maintain it. In the present specimen portions of it were found in position. It was regularly arranged in 

 a series of rounded knobs in rows, and these protuberances have suggested the generic name. 



Near the head the dermal ossifications were quite small, and those preserved are quadrangular in form and arranged 

 in rows. The external surface is peculiarly marked by a texture that appears interwoven like a coarse cloth. This has 

 suggested the specific name, and is well shown in the cut below [fig. 120]. 



The fore limbs are especially massive and powerful, and are much like those of the Jurassic Stegosaurus. There were 

 five well-developed digits in the manus, and their terminal phalanges are more narrow than usual in this group. The ribs 

 are T-shaped in transverse section, and thus especially adapted to support the armor over them. The caudal vertebrae are 

 more elongate than those of Stegosaurus, and the middle caudals have a median groove on the lower surface of the centrum. 



The animal when alive was about 30 feet in length. The known remains are from the middle Cretaceous of Wyoming. 



From the above quotation it is clear that Marsh at that time considered this genus and 

 species as belonging to the Stegosauria. From the title of his paper ("Notice of Gigantic 

 Horned Dinosauria from the Cretaceous") and the context of the text, however, it is also 

 evident that he then included Nodosaurus in the Ceratopsidse, which he at that time con- 

 sidered as a family of the Stegosauria. A few months later, however," he removes this genus 

 from the Ceratopsidse, making it the type of a new family, the Nodosaurida?. He now includes 

 the families Ceratopsidse and Nodosaurida? in a single group, the Ceratopsia, which in the 



introductory paragraph of his article he regards as 

 a suborder, but in the classification of American 

 Cretaceous dinosaurs with which he closes his paper 

 he makes this group of ordinal rank and makes no 

 mention of the Stegosauria. It is clear, therefore, 

 that he at that time regarded the Ceratopsia and 

 Stegosauria as pertaining to distinct orders or sub- 



Fig. 120.— Dermal ossicles of Nodosaurus Uxtilis Marsh. , . . , ■-,-,-,,-, -» T i • i • . i 



Natural size. After Marsh. orders, and that he included the rs odosaurida? in the 



Ceratopsia rather than the Stegosauria. His classi- 

 fication of American Cretaceous dinosaurs as then proposed is as follows: 



The American Cretaceous dinosaurs now known represent several well-marked families, which may be arranged as 

 follows : 



Order Theropoda. Carnivorous. 



(1) The Dryptosauridee, including the large carnivorous forms, of which only imperfect specimens have been found, 

 but sufficient to indicate that they are distinct from the Megalosauridse. of the European Jurassic. Limb bones hollow. 

 Fore limbs very small. Feet digitigrade. with prehensile claws. 



Order Ornithopoda. Herbivorous. 



(2) The Trachodontidse, herbivorous forms of large size, with teeth of the Hadrosaurus type, in many rows. Cervical 

 vertebrae opisthoccelian. Limb bones hollow. Fore limbs small. Feet digitigrade. 



(3) The Claosauridse. Only a single row of teeth in use. Cervical vertebras opisthocoelian. Limb bones solid. Fore 

 limbs small and feet ungulate. 



(4) The Ornithomimidse. Limb bones hollow. Fore Jimbs very small; hind limbs of avian type. Feet digitigrade 



and unguiculate. 



Order Ceratopsia. Herbivorous. 



(5) The Ceratopsidx. Highly specialized forms fully defined above. 



(6) The Nodosauridse. Heavy dermal armor. Bones solid. Fore limbs large. Feet ungulate. 

 No Sauropoda are known from the American Cretaceous. 



Although in the above classification Marsh treated the Ceratopsia as a distinct order, yet 

 a year later, b in the text of a paper accompanying a restoration of the skeleton of Trieeratops, 

 he remarks- 



This group, so far as at present investigated, is very distinct from all other known dinosaurs, and whether it should 

 be regarded as a family, Ceratopsidse, as first described by the writer, or as a suborder, Ceratopsia, as later defined by him, 

 will depend upon the interpretation and value of the peculiar characters manifested in its typical forms. 



a Am. Jour. Sci., 3d ser., vol. 39, May, 1890, p. 425. . 6 Am. Jour. Sci., 3d ser., vol. 41, Apr., 1891, p. 340. 



