NO. 3 NEW CF.RATOPSIAN DINOSAUR GILMORE 5 



The true extent of the postfroiitals in the Ceratopsian skull is here 

 correctly determined for the first time. Authorities have heretofore 

 considered the post frontal as extending from the median line out- 

 ward and including all of that portion of the skull here designated 

 as postf rental and postorbital (see pi. 2). In this specimen a longi- 

 tudinal suture just internal to the base of the supraorbital horn 

 core separates it into two distinct elements. The inner portion all 

 paleontologists agree in calling the postfrontal, the outer appears 

 without question to represent the postorbital. Von Huene/ in 191 2, 

 in a skull of Triccratops prorsus regarded that portion forming the 

 posterior boundary of the orbit as representing the whole of the post- 

 orbital, but the writer now questions the correctness of this determi- 

 nation in the genus Triccratops, in so far as regarding it as repre- 

 senting the entire postorbital. 



In Brachyceratops the postfrontal is a somewhat irregularly trian- 

 gular bone, longer than wide, which unites by suture on the median 

 line Avith'its fellow of the opposite side. 



Anteriorly the combined postfrontals terminate in a pointed pro- 

 jection that is interposed between the deeply emarginate posterior 

 borders of the prefrontals. Posteriorly and on either side of the 

 postfrontal foramen these bones articulate by suture with the median 

 element of the frill. A toothed external border unites with the post- 

 orbital. Beginning between the horn cores the median upper sur- 

 faces of the postfrontals are angularly depressed, gradually deepen- 

 ing and widening transversely as they approach the fontenelle much 

 as in Styracosaurus alhertcnsis Lambe, see E, plate II, The Ottawa 

 Naturalist, Vol. 27, 1913. 



The postorbital gives rise to the small supraorbital horn core and 

 forms nearly one-half of the orbital border. Posterior to this horn 

 which is situated on the extreme anterior end, the bone flares out 

 into a wide expanded portion, much deflected externally, with a 

 curved posterior border, the inner half of which forms a portion 

 of the outer boundary of the supratemporal fossa, the outer half 

 having an underlapping sutural edge for articulation with the squa- 

 mosal. The straight inferior edge meets the jugal which is missing 

 in this specimen. 



The thickened anterior border shows a sutural edge for union with 

 the missing supraorbital bone. On the median inferior surface is 

 a shallow pit which receives the outer end of the alisphenoid, as it 

 does in Stegosaitnts and Camptosaurus. 



' Neues Jahrbuch, 1912, fig. 3, p. 151. 



