74 



THE CERATOPSIA. 



bar of the parietal. It is but 170 mm. in length, and indicates that the squamosals were short, 

 not very broad, and rather inconspicuous as compared with the same elements in some other 

 contemporaneous and later forms. Among the latter may be mentioned more especially Tri- 

 ceratops. Cope's description of the squamosals is somewhat indefinite and does not appear 

 to have been based on any material pertaining to the type. 



The left frontal bone (No. 3997, American Museum of Natural History) mentioned by Cope 

 does not, I am satisfied, belong to the same but to a smaller and younger individual than the pari- 

 etals just described. This conclusion is borne out by the fact that Cope made no mention of this 

 remarkably characteristic element in his original description of the species, and only associated 

 it with the type in his subsequent paper published thirteen years later. Not only is the border 

 for contact with the parietal shorter than that in the parietals, but the color, texture, surface 

 markings, and general conformation of the bone all indicate that it pertained to an individual 

 distinct from that to which the parietals pertained. I believe that any characters it may 

 present should not be considered as certainly diagnostic of the present species, for its specific 



identity must, for the present at least, re- 

 main uncertain. I describe and figure this 

 element in this connection not out of re- 

 gard for any certain additional characters 

 it may furnish distinctive of the present 

 genus and species, but rather for the infor- 

 mation which it affords relative to the 

 homologies of certain cranial elements in 

 the Ceratopsia as a group. It may be de- 

 scribed as consisting of both those elements 

 which have been described and figured by 

 Marsh" as the frontals and postfrontals, 

 but without the slightest indication of a 

 fronto-postfrontal suture, although the 

 sutures for the parietal, squamosal, jugal, 

 prefrontal, and opposing frontal appear in 

 their proper positions on the different mar- 

 gins of the bone. In general form it is tri- 

 angular, with the apex of the triangle di- 

 rected anteriorly. Posteriorly its superior 

 surface is broad, flat, and elevated. Ante- 

 riorly it curves sharply downward and termi- 

 nates in a narrow-pointed projection, which 

 was interposed between the opposite frontal 

 and the left prefrontal. Externally it is much deflected posteriorly, and medially it forms the 

 superior two-thirds of the circumference of the orbit. Immediately above the orbit, at the 

 external border of the postfrontal, there rises a low horn core, broad below and pointed above, 

 with the antero-posterior diameter considerably exceeding the transverse. The external lat- 

 eral surface of this prominence is plane, the internal strongly convex, giving to the horn core 

 the form of one-half of the apex of a cone that has been longitudinally bisected. The orbital 

 border is thick and rugose. The inner border throughout the anterior one-half of its length 

 presents a suture for articulation with the frontal of the opposite side. Posteriorly, however, 

 this border is somewhat emarginate, and instead of presenting a sutural margin it shows a 

 thin, free edge, which formed the lateral border of an elongate foramen, homologous with that 

 which Marsh has designated as the pineal foramen. This expands below into a large cavity, 

 partially inclosed laterally by a vertical septum but apparently communicating with the orbit 

 by one or more small foramina. The posterior border presents an irregular margin for articu- 



«Am. Jour. Sci., 3d ser., vol. 44, 1891, pp. 167-168, PI. I. 



Fig. 76. — A, Oblique front view of frontal and postfrontal (No. 3997, 

 American Museum of Natural History) of Monoclonius crassusf, with 

 supraorbital horn core; B, superior view of same. a. Anterior end; 

 p, posterior; h, supraorbital horn; o, orbit. Both figures are one- 

 fourth natural size. 



