72 THE CEEATOPSIA. 



at that time (December, 1888) was inclined to the opinion that Ceratops Marsh was a synonym 

 of Polyonax Cope, which latter had been founded in 1874 on material collected in the Laramie 

 of Colorado. 



The following year, a in a note entitled "The horned Dinosauria of the Laramie," which 

 did not appear, however, until early in the year 1890 (hence the apparent conflict in dates), 

 Professor Cope was enabled, through the publication by Professor Marsh of a paper (with fig- 

 ures) entitled "The skull of the gigantic Ceratopsidse, " b to determine definitely the homolo- 

 gies of certain bones pertaining to the type of Monoclonius crassus and to define further that 

 genus and species. In this paper Cope proposes the family name Agathaumidse to take the 

 place of Ceratopsidae, previously proposed by Marsh and based on the genus Ceratops, which 

 Cope considered a synonym of some one of the previously established genera pertaining to the 

 family. He concludes this paper by giving a list of the genera and species already known, 

 adding three new species, Monoclonius recurvicornis, M. sphenocerus, and M. Jissus, all of which 

 he describes with more or less detail, unfortunately omitting, however, to include the various 

 forms already described by Marsh. The additional characters then given as diagnostic of the 

 present genus and species, Monoclonius crassus, are so important that I can not refrain from 

 quoting him in full in this connection. 



After giving due credit to Professor Marsh for the assistance rendered by the latter' s article 

 just referred to, Cope continues: 



The most complete skeleton in my collection is that of the Monoclonius crassus Cope. This includes representatives of 

 all the elements except the bones of the feet. The posterior part of the skull is preserved, including the left frontal bone. 

 This bears a horn over the middle of the orbit, of small dimensions, and with the apex antero-posteriorly compressed. • The 

 parietal bones are enormously expanded and are interrupted on each side of the middle line by a huge foramen, which causes 

 the remaining parts of the bone to resemble the corresponding parts of Chamxleo, depressed in a horizontal plane. The squa- 

 mosals are lateral, and consist of a wide plate with convex external border with a slightly undulating outline. The ilium is 

 remarkably elongate both anterior and posterior to the acetabulum, appropriate to the ten vertebrae which constitute the 

 sacrum. It and the sacrum resemble very closely those of the AgatJiaumas sylvestre Cope, which fact, with the evidence derived 

 from the other vertebras, leaves no doubt that the Agaihaumas is to be referred to the horned herbivorous Dinosauria, with 

 Monoclonius and Polyonax. This family is called by Marsh the Ceratopsida?, but as it is not certain that Ceratops Marsh is 

 distinct from one of the genera previously named I shall call it the Agathaumidae (or hellenice Agathaumantidae) from the 

 longest known genus Agaihaumas. 



In a later article entitled "Notes on the Dinosauria of the Laramie," 6 ' Cope considers 

 Ceratops Marsh a synonym of Monoclonius Cope, and distinguishes this genus from Polyonax 

 Cope (Triceratops Marsh, according to Cope) by the relative lengths of the frontal and nasal 

 horn cores, Monoclonius being characterized by short frontal and elongate nasal horns and 

 Polyonax by long frontal and comparatively short nasal horns. In this paper Cope also iden- 

 tifies as cervicals the three coossified vertebrae which he had described in 1876 as anterior dor- 

 sals. He also here announces for the first time the presence of a postpubis, which had been 

 supposed by Professor Marsh to be absent in these dinosaurs. 



DESCRIPTION OF TYPE SPECIMEN. 



With this brief historical review of the synonymy and original and subsequent descriptions 

 of Monoclonius, I will proceed to a detailed description of the type specimen (No. 3998) as it 

 now exists in the collections of the American Museum of Natural History, New York City. 

 In Cope's original description of this genus and species he mentions the teeth, caudal verte- 

 brae, the three anterior dorsals (now known to be the cervicals), the fore limbs, the femur, 

 tibia, ilium, sacrum, and the episterum (now known to be the parietals). 



Owing to the fact that Professor Cope failed to employ any definite marks or symbols for 

 distinguishing type specimens, and the confusion existing in his collection prior to its removal 

 from .Philadelphia to New York, I am unable to identify all the material mentioned by him 

 as pertaining to the type of the present species. In his remark that the most complete skele- 



oAm. Naturalist, vol. 23, Aug., 1889, pp. 715-717. 



b Am. Jour. Sci., vol. 38, Dec, 1889, pp. 501-506, PI. XII. 



cAm. Naturalist, vol. 23, Oct., 1889, pp. 904-906. 



