[lambe] crest of the HORNED DINOSAUR CENTROSAURUS 7 



coalesced parietals, the squamosals being confined to the antero-lateral 

 edge of, and taking liiit little ]\art in the fornuvtion of, the frill. That 

 the large oval fontanelles were included entirely within the parietal 

 part of the expansion and that epoccipital bones were well developed, 

 of which the hinder pair were greatly modified so as to form large hooks 

 or spurs of bone on the hinder border. That a closiely fitting integument 

 was present, as is indicated by the many impressions of blood-vessels 

 on the upper surface, with the probability that the projections of the 

 peri])hery, at the sides and behind, were sheathed in horn. 



The frill of Moiioclonius canadensis is made known to us through 

 the medium of a very perfectly preserved right squamosal and the for- 

 wardly directed terminal portion of the right lateral posterior extension 

 of the parietal which may have borne some resemblance to the parietal 

 bone, the only known part of the crest, of Monoclonivs hcUi. In tlio 

 type specimen of the latter species the posterior parietal bar is broken 

 ofC at some distance on either side of the median line of the head and the 

 more lateral parts that would correspond with the knpwn piece of the 

 parietal of M. canadensis are missing. The type material on which M. 

 canadensis is based includes the squamosal (Cat. No. 1254 a) and the 

 parietal fragment (Cat. No. 1254 b) above mentioned, with a nasal ^ 

 bone (Cat. No. 1254 c), a supraorbital horn core (Cat. No. 1354 d), a 

 ramus of the lower jaw (Cat. No. 1254 e), and an anterior dorsal 

 vertebra (Cat. No. 1254), all of which were found together and pre- 

 sumably belong to the same individual. A maxilla (Cat. No. 285), a 

 lower tooth (Cat. No. 187), a ramus of a lower jaw (Cat. No. 284), and 

 a supraorbital horn core (Cat. No. 212) from the type locality are also 

 mentioned or described in the original description and referred to this 

 species. 



The squamosal, figures 4 and 6, has the form of a moderately 

 thin plate, roughly triangular in shape, the base of the triangle being in 

 front, the apex pointing backward. The outer border is convexly curved 

 in outline, comparatively thick, with an evenly rounded edge, the inner 

 one is concave and sharp-edged. Both the upper and lower surfaces 

 are smooth and few indications of vascular impressions are present. 

 The outer border is undulating, more decidedly so toward the front than 

 posteriorly, there being four well defined convex projections in front 

 with two longer but less salient ones behind; its anterior termination 

 is pointed. The front border has two deep emarginations in its outer 

 half, within it is thin and irregular being the edge of the suturai surface 

 of contact with the jugal and the postfrontal. 



* Originally referred to as the jugal. The writer wishes to express his 

 obligations to Mr. Hatcher, of the Carnegie Museum, Pittsburgh, to whom he 

 is Indebted for a better understanding of the true nature of this bone. 



