Sbction IV., 1904 [ 3 ] Trans. R. S. C 



1. — On the squamoso-parietal crest of the horned dinosaur Oentro- 



saurus apertus and Monoclonius canadensis 



from the Cretaceous of Alberta. 



By Lawrence M. Lambe, F.G.S. 



(Read June 22, 1904.) 



Munoclonius daivsoni and M. canadensis were described by the 

 writer in 1902 in part II of volume III (quarto) of Contributions to 

 Canadian Paleontology ^ from material derived from the Belly River 

 series of Red Deer river, Alberta. The specimens on which the former 

 species was founded consist of an imperfect skull (Cat. No. 1173), 

 figure 14, p. 58, op. cit., and a positerior crest with a nasal horn core 

 (Cat. No. 971), figure 15, p. 59, op. cit. These remains were thought 

 to belong to the same species, but it has since become evident that the 

 separate posterior crest and horn core belong to a distinct species and 

 probably also to a different genus. As the skull was referred to first 

 in the original description and, although poorly preserved, supplies 

 information regarding a number of the cranial elements, it is retained 

 as the type of Monoclonius dawsoni. For the form represented by the 

 posterior crest the writer has proposed" the generic name of Centro- 

 saurus in allusion to the remarkable inwardly directed hook-shaped pro- 

 cesses springing from the posterior border of the frill. The species has 

 been designated by the name apertus in reference to the very large 

 openings or fontanelles lying wholly within the parietal expansion. 



In Monoclonius canadensis the openings in the posterior crest are 

 bounded on the outer side by the squamosals as well as by the parietals 

 and are probably even proportionally larger than those of Gentrosaurus. 



The crests of these two Ceratopsids are so remarkable in their struc- 

 tural characteristics that it is thought desirable lo refer to them at the 

 present time at greater length than was possible when originally de- 

 scribed, and to provide figures for the better illustration of the 

 specimens. 



The crest or frill of Centrosaurus is composed mainly of the 

 coalesced parietals which form an expansion broader than long and 

 decidedly saddle-shaped, with a large opening on either side of the 

 longitudinal axis. The parietal expansion, for the purpose of descrip- 

 tion, may be said to consist of a longitudinal central or axial part, a 

 transverse portion forming the posterior border, and lateral or alar 

 extensions that complete the sides and front margin. The central portion 

 is comparatively broad, is high in front, concave in a longitudinal direc- 



^ On Vertebrata of the Mid-Cretaceous of the Northwest Territory. 



* The Ottawa Naturalist, Vol. XVIII. pp. 81-84, plates I and II, July, 1904. 



