MONOCLONIUS CANADENSIS. 93 



It is extremely massive and only moderately compressed. It curves rather more strongly 

 forward than does the nasal horn of M. dawsoni in the opposite direction or backward. 



One half of a horn core, split longitudinally ° and found with the peculiar parietal (No. 

 971, Geol. Surv. Canada) referred by Lambe, though I think erroneously, to M. dawsoni, 

 appears to represent one half of a nasal horn of the type described by Cope as M. sphenocerus. 

 Owing to the imperfect nature of this specimen it is not possible to determine positively 

 whether it represents a nasal or a supraorbital horn core. It seems more than probable that 

 the type of parietal shown in fig. 91 was associated with a nasal horn similar to that of M. 

 sphenocerus. If this horn core should prove to be a supraorbital the evidence would be equally 

 in favor of excluding it and the associated parietals from the present species in which the supra- 

 orbital horn core is very rudimentary. It seems quite probable that this peculiar parietal 

 may pertain to M. sphenocerus. From the nature of the associated horn core it can not pertain 

 to M. dawsoni. b 



Monoclonius canadensis Lambe. 1902. 



Type (No. 1254 a, b, c, d, e, Geol. Surv. Canada) consists of anterior dorsal and fragments of skull. 



Original description in Contr. Canadian Pal., vol. 3 (quarto), pt. 2, 1902, pp. 63-66. 

 Lambe, L. M., Contr. Canadian Pal., vol. 3 (quarto), pt. 2, 1902, pp. 68, SI ; Ottawa Naturalist, vol. 18, pp. 81-84; Trans. Roy. 



Soc. Canada, 2d series, vol. 10, sec. 4, pp. 3-9. 

 Osborn, H. F., Contr. Canadian Pal., vol. 3 (quarto), pt. 2, 1902, pp. 14, 20. 



a When Mr. Hatcher saw this horn core it was partially embedded in the matrix; on being entirely removed from the latter, the bone was 

 found to be complete and not split longitudinally, as both Hatcher and Lambe supposed. (See PI. XXIV, rig. 3.)— R. S. L. 



6 Centrosaurus apertus Lambe. 1904. 



Type No. 971, Canadian Geological Survey, consisting of a parietal crest and nasal horn core. 



Original description in Ottawa Naturalist, vol. IS, July, 1904, pp. 81-84. 

 Lambe, L. M., Trans. Royal Soc. Canada, 2d ser., vol. 10, 1904, see. 4, pp. 3-9. 



The material upon which this genus and species is based was originally referred to Monoclonius dawsoni and was described and figured as 

 such by Lambe in Contributions to Canadian Paleontology, vol. 3, pt. 2, 1902, pp. 58-59. The type was found in the Belly River (Judith River) 

 series of Red Deer River, Alberta. The author's original description is as follows: 



" The crest of C. apertus is composed principally of the coalesced parietals which form an expansion having somewhat the shape of a 

 saddle, broader than long and much more robust posteriorly than in front where the bone is decidedly thin. The squamosal is not known. 

 The parietal part of the expansion, figs. 1 and 2, PI. I [PI. XXIV], is longitudinally ridged in the median line, is broadly expanded laterally on 

 either side, and ends posteriorly in a robust transverse bar that is concave in outline behind as viewed from above. The fontanelles occur 

 one on either side of the median line and are of large size; they are bounded behind by the transverse bar that forms the posterior border of the 

 crest, and laterally and in front by the thin side extensions. Along the median line the bone is transversely concave beneath. The separate 

 ossifications, named by Marsh epoccipitals, are well developed in four pairs, with, in addition, the pair of hooked processes, already mentioned, 

 which are regarded as specially developed epoccipitals. The alar extensions are referred to in the original description as the squamosal por- 

 tion of the crest, the squamosals being then regarded as having coalesced with the parietals. Near the anterior border of the right extension, 

 however, there is a definite line of demarcation, a, figs. 1 and 2, which can be considered only as the suture for the squamosal. * * * The 

 postfrontal suture, .6, figs. 1 and 2, extends from the inner side of the anterior end of the fontanelle obliquely forward and inward to the median 

 line in front. Numerous impressions of blood vessels are present on and in the neighborhood of the epoccipitals and hooked processes and 

 on the upper surface along the median ridge. 



" The horn core, fig. 3, found with the crest is presumably a nasal one. It is straight and laterally compressed so as to be lenticular in 

 cross section, presenting a sharp edge to the front and rear. A somewhat similarly shaped nasal horn core has been described by Cope under 

 the name Monoclonius sphenocerus. One side, that figured, is deeply channeledlongitudinally ; the other is more regularly convex; vascular 

 markings are conspicuous on both sides. There is apparently no great, distortion, if any, of the specimen, which is 30 centimeters long and 

 imperfect at the tip and below. 



• ' We may conclude from the above that Centrosaurus apertus had a broadly expanded squamoso-parietal crest composed mainly of the 

 coalesced parietals, the squamosals being confined to the antero-lateral edge of, and taking but little part in the formation of, the frill; that 

 the large oval fontanelles were included entirely within the parietal part of the expansion and that the 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 closely fitting integu- 

 ment was present, as is indicated by the many impressions of blood vessels on the upper surface, with the probability that the projections of 

 the periphery at the sides and behind were sheathed with horn." 



In his second paper on this species Lambe gives the following: 



Principal measurements. 



Mm. 



Extreme length from anterior end of crest (imperfect), medially, to line touching posterior edge of specimen on either side. 616 



Length on median line, from anterior end to posterior border 486 



Semibreadth of specimen on curve of under surface 470 



Semibreadth of specimen horizontally 43 " 



Vertical drop of lateral edge of specimen below median line of upper surface at mid-length 186 



Antero-posterior diameter of fontanelle 296 



Transverse diameter of fontanelle 248 



Circumference of base of left posterior spur 172 



Mr. Lambe's description of this interesting type is mainly due to Hatcher's suggestion that it represents a distinct genus and species from 

 Monoclonius dawsoni.— R. S. L. 



