TRICERATOPS HRKVICORNUS 119 



There is a -ingle brow horn, No. 4842 U.S.N.M., which pertains to one of the individuals 

 making up the greater part of the mounted skeleton. It was figured in the Ceratopsia Mono- 

 graph," 7 and was referred by Marsh to prorsus but, as Hatcher says, resembles more nearly the same 

 element in l'ri< era tops elatus. 



Tr'n cramps prorsus is a very popular name, and is used repeatedly in identifying material, but 

 on the other hand, the species seems to have been rare, for but one skull, and that the type, is 

 referable to it without question. 



Triceratops brevicornus Hatcher 08 



Holotype: 9 " No. 1834 Y.P.M.; skull and partial skeleton. 

 Horizon: Lance formation, No. 9 in the sequence. 

 Locality: Niobrara County, Wyoming. 

 Collector: Hatcher, Utterback, Sullins, Bostwick, 1891. 



The skull, which is that of an old individual, is 5 feet 8 inches long, and hence larger than 

 prorsus but smaller than the average of 6 feet 4 inches. The skull proportions resemble those of 

 prorsus, except that the muzzle is relatively longer in proportion to the face. The dorsal profile 

 of the entire skull forms a more or less continuous line, the crest rising in a gentle curve toward the 

 rear. The rostral is proportionately very heavy, with a deeply excavated inferior surface; the 

 cutting edge is rather sharp, but comparatively straight, although pointing downward toward the 

 tip. The descending limb of the jugal is narrow and parallel-sided, while the rather blunt median 

 keel divides the jugal into equal halves. The jugal slopes gently backward. The jugal notch is deep 

 and wide, and the infratemporal opening is large and triangular, with the rounded apex behind. The 

 orbit is an elongated ellipse, with the long axis forming an angle of about 15° with the perpen- 

 dicular. The nasal horn is short and very stout, rather prominent, but smaller than in prorsus, 

 and it does not extend forward over the rostrum as in the latter species. The long diameter is much 

 greater than the transverse. The dorsal profile of the horn core is continuous with that of the nasal 

 bones and sweeps upward in a gentle curve into that of the horn. The anterior margin is somewhat 

 convex, and is inclined slightly forward toward the tip of the horn. 



The brow horns are short, stout, and abruptly tapering, more nearly circular at the base than 

 in any other species, except the specimen of elatus, No. 2100 U.S.N. M. Contrasted with the longer 

 horns of prorsus and horrtdus, they curve gently forward and outward. 



The crest of brevicornus is not very long, being proportionately shorter than in prorsus, and not 

 so sharply curved transversely as in the latter species. The two crests resemble each other in having 

 the dorsal profile undulating and slightly concave, and in the possession of the limited zone of 

 vascular impressions on the under side; the latter is also true of No. 2100 U.S.N. M., mentioned 

 above. The number of epoccipitals is 19 for prorsus, and apparently 17 for brevicornus. The 

 number of maxillary teeth also corresponds at 30. The mandible is of medium proportions, the 

 coronoid process is rather low and not much expanded at the summit, in contrast to that of prorsus 

 which is high with a marked expansion. The predentary is heavy to match the jaw, and rather 

 sharply pointed. 



The preorbital fossa seems to lie entirely within the maxillary, although the ill-defined sutures 

 make this difficult to determine with certainty. 



But one other skull known to me seems referable to this species and that was collected by 

 Mr. W. H. Utterback in the Hell Creek region of Montana, in 1904, and is now preserved in the 

 Carnegie Museum in Pittsburgh. This skull conforms with the type except for certain minor varia- 

 tions as follows: Length over-all is 6 feet 3 inches as compared with 5 feet 8 inches for the type, 

 though both are aged animals. The nasal horn is somewhat larger and heavier, which brings the 

 center of mass further forward and makes the muzzle appear shorter, although the ratio of muzzle to 



67 Loc. cit., p. 128, Fig. 108. 



88 Hatcher, 1. B.. 1905, p. 413. 



"Hatcher, Marsh, Lull, 1907, Pis. XL1-XL1I. 



