84 THE CERATOPSIA 



crest extending to the rear. Somewhat in advance of the orbits a horn core, of large size and appar- 

 ently symmetrical form, occupied a position suggestive of a nasal origin, the nasal bones and the 

 frontals being probably represented by the fragments filling the space between the orbit and the 

 horn core .... 



"The large posterior crest forms the back part of the skull above; its exact shape is fortunately 

 supplied by the admirably preserved specimen shown in outline, .... [This crest, No. 971 G.S.C. 

 was later made the type of the genus and species Centrosaurus apertus Lambe. 13 ] The surface of the 

 bone, above the orbit and from there inward for a short distance toward the median line of the 

 skull, is moderately smooth and shows no trace of a horn core." The remainder of the description 

 pertains to the second crest. 



It is unfortunate that the condition of the actual crest of this specimen rendered it incapable of 

 preservation and that Mr. Lambe, instead of describing it in detail, should have turned to the other 

 crest to complete his description of the species. So far as the nasal horn is concerned, Lambe's first 

 reference of the species to Monoclonius would be valid, although it is the only known specimen of 

 this genus in which the horn curves backward. In all the other Monoclonius skulls it is either erect 

 or forwardly curved. No other detail debars the type from Monoclonius except possibly the crest. 



The known characters of the species M. dawsoni are as follows: 14 nasal horn large, curved 

 backward; supraorbital horns incipient; squamosals small, smooth undulating margins to crest; 

 epoccipitals absent; parietal fenestrae greatly reduced or absent. If the last statement is true the 

 form cannot be Monoclonius or Centrosaurus. This species has, however, been also referred to 

 Brachyceratops, a genus described by Gilmore from the Two Medicine formation, although evidence 

 for such inclusion is very inadequate. The nasal horns are very different, for in Brachyceratops it 

 was made up of two elements, one derived from each nasal bone and therefore separated in the 

 median plane, a juvenile character known in no other ceratopsian skull except Eoceratops canadensis. 

 A presumable element of agreement lies in the apparently small size of the parietal fenestrae and the 

 general form of the squamosals, with their undulating border and lack of epoccipital bones. The 

 shape of the orbit is somewhat similar in each form. The actual form of the crest which belonged 

 to the type skull, at present vaguely understood, will determine the generic status, and not until 

 another undoubted specimen is found can the real position be known. Tentatively, I would leave 

 the form as Lambe originally named it. 



Sub-genus CENTROSAURUS Lambe (Belly River phase) 



This sub-genus was founded upon a parietal crest first described by Lambe 1 " in conjunction with 

 the Belly River type of Monoclonius dawsoni. The latter consisted of an extremely fragmentary 

 skull, No. 1 173 G.S.C, discovered by Lambe in 1901, but in such condition that the crest could not 

 be preserved, so that the one under discussion, No. 971 G.S.C, was considered part of the type, 

 although from a somewhat different locality and level, and was used in the original description; 

 no record was taken of the actual crest other than a rather vague, though measured, field sketch 

 made before the parts were removed. 16 From this sketch it is evident that Monoclonius dawsoni had 

 a different type of crest from that of Centrosaurus apertus and that Lambe was justified in erecting a 

 new genus for the inclusion of the latter. But the species of Centrosaurus are confused in the same 

 way as are those of Monoclonius, since in each genus the genoholotype is based on a crest only, which 

 cannot be compared with the same element in the types of the other species, because these types 



"Lambe, L. M., 1904, p. 81. 



14 Lambe, L. M., 1915, p. 21. 



15 Lambe, L. M., 1902, pp. 58-59, also Hatcher, Marsh, Lull, 1907, p. 89, Fig. 92. 



10 In a letter to the present author dated May 30, 1905, and published in the Ceratopsia Monograph, page 179, 

 Mr. Lambe places the type of Centrosaurus afertus, No. 971, in what he calls the Lower (primitive mammal) beds with 

 Eoceratofs canadensis; while Monoclonius dawsoni, No. 1173, is referred to the Middle beds, and Chasmosaurus belli to 

 the Upper. Centrosaurus afertus was collected on the west side of Red Deer River, July 26, 1901, while Monoclonius 

 dawsoni came from the east side, August 1 5 of the same year. 



