168 THE CERATOPSIA. 



CENTROSATJRTJS. 



1. Centrosaurus apertus Lambe (p. 93, footnoted; fig. 93; PI. XXIV) is based upon a parietal 

 crest and an associated nasal horn core (No. 971, Canadian Geological Survey), and no specific 

 distinctions need be reviewed. 



AGATHAUMAS. 



In the genus Agathaumas Hatcher retains but one species, A. sylvestris Cope, the other, 

 A. milo Cope, having been referred later by its author to Hadrosaurus occidentdlis. Hatcher 

 sums the matter up by adding: "Whether or not this determination was correct the fact 

 remains that A. milo is a nomen nudum, and the fragmentary nature of the type precludes 

 adequate description. The species should therefore be discarded." 



1. Agathaumas sylvestris Cope. — The characteristics of Agathaumas sylvestris (pp. 105-111, 

 PI. XXV) have been discussed under the generic summary. 



DICERATOPS. 



1. Diceratops hatcheri Lull. — This genus contains but one species, D. hatcheri, described 

 but left unnamed by Mr. Hatcher, based upon skull No. 2412, U. S. National Museum (p. 149, 

 Pis. XL VII and XLVIII). The specific characters need not be cited in this summary, but 

 one species being thus far known. 



TRICERATOPS. 



The present writer recognizes ten species under the genus Triceratops Marsh, a number 

 which he believes to be in harmony with Hatcher's views, though in the case of T. (Sterrholo- 

 phus) flabellatus no final statement by Hatcher has been found. 



These species are as follows: 



1. T. (Ceratops) horridus Marsh. 6. T. sulcatus Marsh. 



2. T. prorsus Marsh. 7. T. elatus Marsh. 



3. T. brevicornus Hatcher. 8. T. calicornis Marsh. 



4. T. serratus Marsh. 9. T. (Sterrholophus) fldbellatus Marsh. 



5. T. {Bison, Ceratops) alticornis Marsh. 10. T. obtusus Marsh. 



Thus three species have been brought into the genus, two from Ceratops and the only 

 species of Sterrholophus, which becomes synonymous with Triceratops. One species, T. galeus 

 Marsh (p. 132, fig. Ill), which was based upon a single horn core that resembles most the 

 same structure in Torosaurus gladius, Hatcher decided to abandon on the ground of the frag- 

 mentary nature of the specimen. 



1. Triceratops horridus Marsh (pp. 117-122, figs. 24, 25, 27, 107, PI. XXVI) , the type species, 

 is based upon the imperfect skull of a huge individual, No. 1820, Yale Museum, fully adult 

 and very old. 



The rostral bone is very heavy, not so sharp along its inferior border as in some species, 

 downward curved toward the tip, with deerj vascular impressions. 



The nasal horn core (PI. XXVI) is very broad at the base, short and blunt in contrast to 

 that of the most nearly allied species, T. prorsus, in the type of which the nasal horn is long 

 and directed forward, and T. brevicornus, in which it is short and very stout but not highly 

 rugose. This contrast is the more interesting because the types of all three species were aged 

 individuals. 



The supraorbital horns in T horridus are exceedingly stout and rugose, long, and directed 

 forward as in T. prorsus, in contrast to the extremely short horns of T. brevicornus. The great 

 size of T. horridus as compared with either T. prorsus or brevicornus is an important distinction. 



2. Triceratops prorsus Marsh (pp. 127-132, figs. 35, 37,40,41,49-58, 63-67, 71, 109, 110, Pis.. 

 VI-XVII, XXX-XXXVI) is an example of the opposite extreme in size from T. horridus, 

 the type skull, No. 1822, Yale Museum, that of an aged individual, being one of the smallest 

 of the Laramie Ceratopsia. 



The rostral bone is contrasted with that of T. horridus in being somewhat less massive and 

 having a sharp cutting edge, as contrasted with the blunt margin in the other. The inferior 

 margin curves downward toward the point, in agreement with T horridus and T. brevicornus. 



