34 



THE ROYAL SOCIETY OF CANADA 



The compactness of the parieto-frontal complex, and the denseness 

 of the bones of which it is composed accounts for the frequent pres- 

 ervation of this part of the skull. Of the twelve or more specimens 

 collected, all, with the exception of the one described and figured in 

 this paper. Cat. No. 138, consist only of the thickened coossification of 

 parietals and frontals from which the squamosals, postorbitals, and 

 the more anterior bones bordering on the frontals forward to and 

 including the nasals had dropped off, some evidently before the cen- 

 tral mass had come to rest and been buried in sand or clay. 



That Stegoceras attained a much larger size than is indicated by 

 the specimen Cat. No. 138 is shown by the largest and most massive 

 specimen collected, Cat. No. 192, which is nearly twice as thick and 

 broad as No. 138. 



The proportion of thickness of the parieto-frontal mass, at the 

 parieto-frontal suture, to its breadth at the same suture in a number 

 of specimens is as given below, all of the specimens with the exception 

 of No. 138 consisting of the parieto-frontal mass only. 



From the above measurements it is seen that the relative thick- 

 ness of the bone above the brain varies to some extent. It is constant 

 at about two-thirds of the breadth in the first five specimens which in- 

 clude the very large one No. 192. In specimen No. 121, referred to a 

 proposed new species 5*. brevis (see p. 35), there is a slight variation, 

 and in the last two, the thickness is noticeably less. 



A specific determination of the above specimens is not attempted 

 now, except in the case of Nos. 138 (S. validus) and 121 {S. brevis) 

 which are more comprehensive and better preserved than the others, 

 and supply the data necessary, in the present state of our knowledge 

 of the genus, for such a determination. 



Stegoceras is a diapsidan reptile differing from any described form, 

 but apparently approaching most closely the Stegosaitridœ {Stego- 



