6 



THE CEEATOPSIA. 



portions of the skulls of the first two of these species were given, and also a figure of the parietal 

 of M. crassus, which had previously been described by Cope first as an episternal and later 

 figured and described by him as a sternal. 



REMAINS OF CERATOPSIA DISCOVERED BY CANNON, ELDRIDGE, AND CROSS. 



In 1887° Marsh described and figured a pair of horn cores discovered by Mr. George L. 

 Cannon in the light-colored sandstones of the Denver beds on Green Mountain Creek, near 

 Denver, Colo. These remains were at first referred by Professor Marsh to the bisons and 

 described under the name of Bison alticornis, and on this evidence alone the deposits were 

 determined by him to be more recent than the Equus beds (now universally considered Pleisto- 

 cene), and probably late Pliocene. It is now well known that Professor Marsh erred in referring 



these remains to the bisons, and 

 that they are in reality the 

 supraorbital horn cores of one of 

 the larger Ceratopsia. Nor is 

 Professor" Marsh's error to be 

 wondered at, but on the other 

 hand it is quite excusable, since 

 at that time nothing was known 

 regarding the structure of the 

 skulls of these strange dinosaurs, 

 and in size, surface markings, 

 and form these horn cores more 

 nearly resembled those of certain 

 extinct bisons than of any other 

 known animals, while the very 

 imperfecta petrified nature of 

 the remains might very readily 

 be taken as indicative of the 

 Pliocene or Pleistocene age of the 

 deposits. Indeed, this mistaken 

 identification is a striking ex- 

 ample to show how occasionally 

 one may the more readily be led 

 into error through a complete 

 familiarity with his subject, for 

 all that was then known of 

 comparative osteology, as well 

 as the superficial structure and 

 general character of the remains 

 indicated that these horn cores 

 pertained to a very large extinct 

 bison. Had the remains fallen into the hands of any other vertebrate paleontologist prob- 

 ably the same error would have been made, for prior to the discovery of the complete skulls, 

 which occurred a few j^ears later, nothing short of a microscopical examination of the minute 

 structure would have revealed their reptilian nature. Through the later discovery of more 

 perfect material Professor Marsh was able, about two years later, to determine the true nature 

 of these remains, and in 1889 c provisionally referred them to the horned dinosaurs under the 

 name Geratops alticornis. 



" The sternum of the Dinosauria: Am. Naturalist, 1886, pp. 153-155. 



& Notice of new fossil mammals: Am. Jour. Sci., 3d ser., vol. 34, October, 1S87, pp. 323-324. 



c Notice of gigantic horned Dinosauria from the Cretaceous: Am. Jour. Sci., 3d ser., vol. 37, August, 1SS9, pp. 173-175. 



Fig. 4. — Occipital region of Monoclonius rceurvicornis. Figured hut not identified by 

 Cope in 1877. A, Right lateral aspect: B, posterior asp?ct; C, inferior aspect, oc. Occip- 

 ital condyle; exo, exoceipital; bo, basioccipital; fm, foramen magnum. One-fourth 

 natural size. After Cope. 



