84 0. C. Marsh — Skull of Torosaurus. 



The small dinosaur, about as large as a Rhinoceros, for which 

 the name Monoclonius was proposed, is perhaps generically 

 distinct from Agathaumas, but no conclusive evidence of this 

 has yet been presented. The description given makes the teeth, 

 dorsal vertebrae, and pelvis, different from those of any of the 

 larger forms, and the T-shaped parietal (figured first by Cope 

 as an episternal bone), is especially distinctive. None of the 

 other known Ceratopsidaz have the parietal fontanelles except 

 Torosaurus, one of the most gigantic forms discovered, and 

 this genus differs from Monoclonius, as described, in various 

 important points. The very long frontal horn-cores, directed 

 forward, the narrow, elongate squamosals, the absence of a 

 median crest on the parietal, as well as the form and anterior 

 connections of this bone, all serve to clearly distinguish the 

 former from the latter. 



These points, and others relating to the nomenclature of the 

 Ceratopsidce, will be fully discussed in a later communication, 

 when the large acquisitions recently secured by the writer's 

 able assistant, Mr. J. B. Hatcher, are ready for description. 



New Haven, Conn., Dec. 22, 1891. 



EXPLANATION OF PLATES. 

 Plate II. 



Figure 1. — Sknll of Torosaurus latus, Marsh; seen from above. 

 Figure 2. — Posterior crest of T. gladius, Marsh; seen from above. 



c, supra-temporal fossa ; c', anterior temporal foramen; /', parietal fontanelle; 

 h, horn-core ; h', nasal horn-core ; p, parietal ; s, squamosal. 



Both figures are one-twentieth natural size. 



Plate III. 



Figure 1. — Right squamosal of Torosaurus gladius; inner view. 



Figure 2. — The same of Sterrholophus flabellatus, Marsh. 



Figure 3. — The same of Geratops montanus, Marsh. 



Figure 4. — -Skull of Trictratops serratus, Marsh; diagram; seen from above. 



Figure 5. — Skull of Sterrholophus flabellatus ; seen from behind. 



Figure 6.— Skull of Triceratops prorsus, Marsh; seen from behind. 



d, dentary; d' : epijugal bone; e. epoccipital ; /, frontal ; g, groove for quadrate ; 

 - fP* postfrontal; j, jugal; m, maxillary; n. nasal; pf, prefrontal; pm, 



premaxillary ; s', suture for parietal. 



All the figures are one-twentieth natural size. 



