marsh.] CERATOPSID.E. 217 



AGATHAUMAS. 



Three other generic names have been applied by Cope to remains of 

 Oeratopsidae found in this country, namely, Agathaumas, Polyonax, 

 and Monoclonius. The first of these was based on part of a skeleton, 

 -without the skull, found in Wyoming. The second name was given 

 to various fragments from Colorado, including parts of horn cores, 

 regarded as ischia, but all these may be the same generically as the 

 preceding specimen. The third name, Monoclonius, was used for a 

 skeleton from Montana, with parts of the skull and teeth preserved. 

 This animal was one of the smallest of the group, while the other 

 remains pertained to reptiles of larger size, but not of the gigantic 

 proportions of those more recently described. So far as can be judged 

 from the descriptions and figures of the type specimens, the three 

 generic names just cited can not be used for any of those previously 

 mentioned in this article. A comparison of the principal characters 

 will place this beyond reasonable doubt. 



In the type of Agathaumas the remains best preserved are from the 

 pelvic region, which, according to Cope, 1 possesses the following fea- 

 tures: The ilium has no facet nor suture for the pubis at the front of 

 the acetabulum, and the base of the ischium is coossified with the ilium. 

 There are eight, or perhaps nine, sacral vertebrae, with the neural 

 spines of the first five mere tuberosities. The diapophyses are in pairs, 

 and the last sacral vertebra is reduced and elongate. These charac- 

 ters, and some others found in the description cited, are certainly dis- 

 tinctive, but do not apply to any of the allied fossils described by the 

 writer. Portions of the type specimen, moreover, are in the Yale 

 museum, as well as other remains from near the same locality, The 

 fossils described as Polyonax, and other similar specimens collected in 

 the same region, afford at present no evidence for separation from 

 Agathaumas. 



MONOCLONIUS. 



The small dinosaur 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 

 Ceratopsidse have the parietal fontanelles except Torosaurus, one of 

 the most gigantic forms discovered, and this genus differs from Mon- 

 oclonius, 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 distinguish clearly the 

 former from the latter. 



' Vertebrata of the Cretaceous formations of the West, p. 53. 1875. 



