STEGOCEKAS VALIDUS. 



99 



minute columns of bone arranged perpendicular to and radiating from the external surface of 

 the various bones of the roof of the skull, with which they are firmly coossified at their bases, as 

 shown in fig. 100. 



If my interpretation, which differs only in a few unimportant particulars from that of 

 Nopcsa, is correct, Lambe was not only wrong in considering these elements as prenasals, 

 but he also possibly mistook the anterior for the posterior extremities. I would interpret the 

 large median cavity shown on the inferior surface in fig. 99 as the upper portion of the brain 

 cavity, while the transverse suture which divides it into ante- 

 rior and posterior moieties I would consider the parieto-frontal 

 suture, rather than the fronto-nasal, as believed by Nopcsa. 



Thus the bone in front of the suture becomes, according 

 to my interpretation, the frontal rather than the nasal, as 

 regarded by Nopcsa, though faint lateral sutures just in advance 

 of the interorbital constriction may mark the posterior borders 

 of the nasals. Like Nopcsa, I regard the lateral cavities as 

 orbital. Posteriorly in the larger of the two specimens there 

 are two deep lateral cavities which opened externally by a small 

 circular foramen, only the internal border of which latter is rep- 

 resented in either specimen. The deep lateral cavities I inter- 

 pret as infratemporal fossse, while the circular foramina opening 

 into them may possibly represent the supratemporal fossse, 

 though from the position of these foramina this interpretation 



appears hardly probable. 



On the larger of the two 



more complete specimens 



just behind that cavity 



which I have considered 



the brain cavity there is a 



broken or sutural surface, 



followed by a rather deep median excavation terminating 



anteriorly in two shallow pits separated by a median 



septum. This may have formed the roof of the foramen 



magnum. 

 Without more perfect material it is quite impossible to determine definitely either the 

 homologies of these elements or the nature of the animal to which they pertained. In the 

 present writer's opinion, however, there is no good reason for considering them as horn bearing, 

 or the animals to which they belonged as pertaining to the Ceratopsidse'. I, therefore, do not 

 include them in that group. 



Principal dimensions of bones of Stegoceras validvs. 



For the larger (type specimen No. 515, Geol. Surv. Canada) : Mm. 



Greatest length . 106 



Greatest breadth - - 60 



Greatest depth — - 41 



For the smaller (No. 1423, Geol. Surv. Canada): 



Greatest length - - — 64 



Greatest breadth - - 44 



Greatest depth - 31 



Taken as a whole the collection of Ceratopsia made by Lambe from the Belly River beds 

 is a most important one, since it furnishes much valuable evidence not only regarding the dis- 

 tinctly generic characters of these earlier and less specialized members of the-family, but relating 

 also to the ancestry and phylogeny of the later, more highly specialized, and much better known 



Fig. 99. — Inferior view of Stegoceras validus 

 Lambe, No. 1423, Geol. Surv. Canada. 

 a, Anterior; p, posterior; n, nasai; /, 

 frontal; pe, parietal; so, supraoccipital. 

 Natural size. 



Fig. 100. — Side view of type specimen, No. 515, 

 Geol. Surv. Canada, showing columnar struc- 

 ture of dermal ossification. One-half natural 

 size. 



a See footnote c, p. 98. 



