GENERIC AND SPECIFIC SUMMARY. 17 1 



8. Triceratops calicornis Marsh (pp. 138-139, Pis. XXXVIII-XL) is based upon a large 

 but immature skull, jaw, dorsal vertebrae, ribs, pelvis, sacrum, etc. (No. 4928, U. S. National 

 Museum) . 



The specific affinities would seem to be with the preceding species, T. elatus, from the 

 similarity of both nasal and supraorbital horns and of the frills. The main distinctions lie 

 in the proportions of the skull of the present species, as the premaxillaries are here much longer 

 and the rostral bone larger, with a much fuller anterior curve, thus making that portion of 

 the skull in advance of the nasal horn proportionately much more pronounced. 



The nasal horn core is low, almost vertical, convex in front and concave behind. T. 

 calicornis agrees with T. elatus in having the small nasal horn core sharply marked off from 

 the nasals, not apparently continuous with them as in most species. 



The descending process of the jugal differs from that of T. elatus in being more nearly 

 vertical, as in other species. This may, however, as Hatcher says, be due to difference of 

 pressure in the two types. 



The frill is only in part preserved, but the squamosals are almost entire. They agree 

 with those of T. elatus in lacking marginal undulations and apparently bore but three or four 

 epoccipitals on the posterior portion, which are not ankylosed. The squamosals are longer and 

 narrower, a fact which aids in giving to the entire skull a greater proportionate length than 

 that of T. elatus. The lachrymal foramen is between the nasal and maxillary in both species, 

 thus agreeing with serratus and flabellatus. Hatcher expresses the opinion that T. elatus and 

 T. calicornis may prove synonymous. 



9. Triceratops ( = Sterrholophus) flabellatus Marsh (pp. 143-148, figs. 6, 8-11, 15, 17-23, 28, 

 31, 33, 36, 38, 39, 43, 44, 60-62, Pis. XLIV-XLVI) is known from the nearly complete though 

 disarticulated skull of a very young individual (No. 1821, Yale Museum). This species Marsh 

 made the type of a new genus, Sterrholophus, because of the character of the frill, but, as shown 

 above (p. 164), the peculiar absence of vascular impressions from the latter may be considered 

 an adolescent character, which may also be said of each presumably generic feature exhibited 

 by the skull. 



The nasals are massive, but not yet coossified, nor was the nasal horn core ankylosed, so 

 that this important feature is lacking. 



The supraorbital horn cores are rather long, laterally compressed near the base but more 

 nearly circular in section toward the summit. They are inclined forward and outward at a 

 less angle than in other species. 



The orbit is elliptical and the lachrymal foramen lies entirely within the maxillary bone 

 as in T. prorsus. 



The long axis of the frill exhibits less of an upward curve than in other species except T. 

 serratus. 



The squamosals are rather short and broad, as in T. serratus, though the entire frill viewed 

 from above is proportionately much narrower because it is more highly arched. 



T. flabellatus bore upon its frill the maximum number of epoccipitals known, nineteen, of 

 which six pairs are attached to the squamosals, the remaining seven upon the coalesced 

 parietals. 



10. Triceratops obtusus Marsh (pp. 140-141, figs. 116, 117) is known from portions of a skull 

 (No. 4720, U. S. National Museum) representing a large, adult animal. 



The nasals are very broad and the nasal horn core is reduced to a broad, rounded, rugose 

 prominence marked with a number of deep vascular grooves. 



The dentary is described as exceptionally deep and massive, and the teeth are unusually 

 large. The extreme forward extension of the mandibular fossa seen here is exceptional 

 among Ceratopsia. 



