TRICERATOPS HORRIDUS.' 119 



In this paper Marsh calls attention to the presence of a number of characters hitherto 

 unknown in this or any other group of dinosaurs — such as the strong nasal horn, the os rostrale 

 and the huge occipital crest functioning as a shield for the cervical region — but does not state by- 

 just what characters this genus is to be distinguished from Ceratops, nor is this distinction easy 

 to make, considering the material on which the last-mentioned genus was founded. Never- 

 theless, when we consider the diminutive size of Ceratops in comparison with that of Triceratops 

 and the differences observable in the characters of the frontal horns (compare figs. 5 and 103), 

 it is evident that they may have pertained to distinct genera and that if, in the types of each 

 species, more parts in common had been preserved it would be possible to establish other 

 differences of still greater importance. Moreover, the difference in the geological horizons 

 from which the types of the two genera were derived is so great as to preclude the probability, 

 not to say possibility, of their having pertained to a common genus. The type of Triceratops 

 horridus came from about the middle of the upper half of the Laramie deposits as they are 

 represented in Converse County, Wyo. The type of Ceratops montanus was found near the 

 summit of the Judith River beds in Montana. Between these two series of deposits are inter- 

 calated the Bearpaw shale and the true Fox Hills sandstone, the actual combined thickness of 

 which has yet to be determined, but which, from observations made by the writer on Willow 

 Creek, Montana, could not have been much, if any, less than 2,000 feet. To this should be added 

 the 1,500 feet of sediment lying between the horizon at which the type of T. horridus was found 

 and the top of the Fox Hills, so that a series of deposits aggregating approximately 3,500 feet 

 in thickness separated the strata from which the tj^pes of these two genera were obtained — a 

 series representing an enormous time interval, too long, it is believed, for any single genus of so 

 highly specialized dinosaurs as were the Ceratopsia to have persisted. Considering the differ- 

 ence in time at which they lived and their difference in size and structure, there can be little 

 doubt but that they were generically distinct and that this distinction will be still further empha- 

 sized when more is known of the structure of the genus Ceratops, which is as yet only known 

 from fragments. 



DETAILED DESCRIPTION OF TYPE. 



The type (No. 1820, Yale Museum) of the present genus and species pertained to a fully 

 adult and apparently very old individual. When first seen by the present writer the central 

 mass of the cranium lay embedded in a large concretion of hard, gray sandstone lying on the 

 weathered slope a few feet above the bed of the rather picturesque canyon in which it was found. 

 It had probably rested in its present position for more than a century subjected to the destruc- 

 v tive action of wind and weather. Although numerous fragments of the anterior and posterior 

 portions of the skull lay scattered about over the slope and others were recovered from the 

 loose sand at the bottom, no inconsiderable portion of it had been swept away and irretrievably 

 lost by the torrents of water that in spring and summer rush madly down the usually dry beds 

 of all the canyons of this semiarid region after each recurring storm. It thus happens that 

 in the type of this genus, the most prolific in species and individuals of any of the Laramie 

 Ceratopsia at least, many interesting characters are not shown. 



Although the skull is badly injured by weathering, these injuries are not wholly without 

 their advantages, since they reveal many points in the anatomy of the skull which it would be 

 difficult to determine from a more perfect specimen without duplicating in part, at least, the 

 injury which the present skull has already suffered. 



By weathering, a transverse section of the skull is given just in advance of the orbits, a 

 view of which is seen in fig. 27 (p. 30), which shows well the relations of the frontals, post- 

 frontals, alisphenoids, palatines, pterygoids, maxillaries,. and vomers in this region. The 

 frontals and prefrontals are seen to rest on top of a forward prolongation of the postfrontals 

 which reaches forward in advance of the alisphenoids, probably extending as far as the anterior 

 border of the orbits. Medially in this region the frontals and postfrontals are in contact, but 

 laterally the postfrontals are separated from the overlying frontals and prefrontals by two 

 large cavities, which in fig. 24 (p. 28) are represented as filled with matrix. 



