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THE CERATOPSIA 



circular, as opposed to the usual elliptical shape, but the slightly longer axis slopes, as usual, at an 

 angle of about 45° from the perpendicular. The descending limb of the jugal is narrow and 

 tapering, without a median keel, and the axis is inclined slightly backward. The jugal notch is 

 fairly deep and wide, the infratemporal opening being of average size and somewhat triangular, 

 with curved margins. The rostral is large, although less massive than in horridus, with a sharp 

 cutting edge and downwardly curved inferior margin. The muzzle is rather short, although the 

 face is long. The most distinctive feature of prorsus is the nasal horn, which is long and directed 

 forward so that its tip extends over the forward margin of the rostral, the anterior profile being 

 inclined forward at an angle of 35° from the perpendicular. This nasal horn is unique, and occurs 

 in no other skull, although approaching that of brevicornus and the American Museum skull (No. 

 5028) mentioned above. 



The brow horns are slender, directed upward, outward, and forward for half their length, and 

 then curved gently inward and upward toward their tip. This reversed curve is characteristic of 

 calicorms and elatus, although they both differ from -prorsus in the possession of a rugose promi- 

 nence on the rear of the horn's base. The horns of prorsus are more slender than are those of 

 either horridus or brevicornus, and much longer than the latter. 



The crest is deeply arched, and helmet-shaped, with an undulating dorsal line which is concave 

 upward, the rear third being missing. A characteristic feature which links prorsus and brevicornus 

 is the limitation of the vascular impressions on the inferior surface of the crest to a very clearly 

 defined marginal zone averaging 15-17 cm. in width. There are deep vascular impressions also on 

 the dorsal aspect of the crest, the nasals, and horns. 



The preorbital fossa lies entirely within the maxillary; the ascending process of the premaxil- 

 lary, although long and slender, does not quite reach it. The pseudopineal fontanelle is utterly 

 lacking, in possible agreement with the flabellatus type skull as figured by Marsh, 64 but with no 

 other. This is, apparently, not a matter of age, for the flabellatus specimen is extremely young, 

 and no matter what the age of other skulls, young or old, it is always present. The mandible is 

 rather slender, with a high coronoid process, expanded fore and aft at the summit. The number 

 of vertical rows of teeth is, in the maxillary, about 30, in the mandible, about 33. 



Triceratops prorsus is nearest to Triceratops brevicornus in relationship, agreeing in general 

 proportions, in the presence of the vascular zone around the periphery of the inferior aspect of the 

 crest, and in the rather large nasal horn and its general slope which, however, is greater in prorsus. 

 They disagree in the shorter and stouter brow horns of brevicornus, but their assignment to the 

 same phylum can hardly be questioned. 



Several skulls have been identified as pertaining to this species, notably No. 2100 65 and 

 No. 1205 of the United States National Museum; but there seems to be little warrant for such 

 assignment if the highly diagnostic nasal horn is taken into account, for that of the skull No. 2100 

 is very different in character and is of the elatus type, while No. 1205, a fragmentary skull, possesses 

 none at all in its present mutilated state. 



No. 2100 is the skull now borne on the mounted skeleton, but it is not the one figured in the 

 paper restoration of the animal, published by Marsh, 66 for which he used the type skull of prorsus, 

 now at Yale. The skeleton is a composite one and includes at least ten catalogue numbers and 

 therefore as many, if not more, individual animals. Many of the separate bones were figured by 

 Marsh or Hatcher in discussing the morphology of the Triceratops skeleton, but always called 

 Triceratops prorsus. I have yet to find specific characters in the skeletal elements other than the 

 skull, and see no possible assurance of the correctness of these specific identifications of the separate 

 bones for, aside from skull and jaws, the type of prorsus includes only the six anterior cervical 

 vertebrae and some of their ribs, and it is only by actual association of a specifically identifiable 

 skull and a more or less complete skeleton in two or more instances, that skeletal contrasts of a 

 specific nature can be determined. 



64 Hatcher, Marsh, Lull, 1907, PL XLV. 



65 Hatcher, Marsh, Lull, 1907, Pis. XXX-XXXI. 

 Loc. cit., p. 190, Fig. 125. 



69 



