6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 63 



Immediately above the orbit on the anterior part of the postorbital 

 there rises a low horn core, the upper extremity being obtusely 

 rounded from a lateral aspect, see po.h plate i, but sharply pointed 

 when viewed from the front. The external surface of this horn 

 is plane, the internal strongly convex, with the antero-posterior 

 diameter greatly exceeding the transverse, the total height of the 

 horn above the orbit being 35 mm. These horn cores appear to be 

 outgrowths from the postorbital bones unless they include a posterior 

 supraorbital element such as has recently been found in the skull 

 of Stegosaurns. However that may be, there is no trace of such a 

 division in the postorbitals of this specimen. This again raises the 

 question of the proper designation of these horns which have been 

 called successively postfrontal and supraorbital horti cores. If an 

 outgrowth from the postorbital bone, as the present specimen appears 

 to indicate, the term postorbital horn core would be a more appropri- 

 ate designation. 



The prefrontals (the frontals and lachrymals of autliors) are 

 deeply emarginate anteriorly and receive between them the pointed 

 posterior ends of the nasals. 



The prefrontal is a c|uadrangular plate of bone diagonally placed 

 filling the interspace between the postfrontal and nasal bones. Its 

 thickened posterior end contributes to the inner part of the anterior 

 boundary of the orbit. Near the posterior termination a narrow 

 vertical sutural surface {so, pi. 2) on the external side was for the 

 articulation of the small supraorbital bone that is missing. This ele- 

 ment would have completed the thickened projecting orbital border 

 immediately in front of the eye and which forms such a conspicuous 

 feature of the Ceratopsian skull. On the upper posterior end of the 

 prefrontal a pointed peg-like projection is received in a correspond- 

 ing pit in the anterior border of the postfrontal, thus strengthening 

 the union of these two bones. The prefrontal is just barely in con- 

 tact with the postorbital at the base of the postorbital horn core. 



The relationships of the pre- and postfrontals in Brachyccratops is 

 an unusual one, for in most dinosaurian crania the frontal is inter- 

 posed between them, and so far as the writer is aware the above 

 condition is only found in Stegosaurus among the dinosauria and in 

 •some of the Permian reptilia. Von Huene has shown, and the writer 

 believes correctly too, that the frontal in Triceratops has been en- 

 tirely excluded from the dorsal surface of the skull. 



The frill is represented by the median elements from two individu- 

 als. Both have portions missing, but the better preserved one is 



