70 THE CERATOPSIA. 



From the order in which he took up anc 1 described the various genera of dinosaurs in his 

 original description of this genus it is clear that Cope did not at that time regard Dysganus as 

 being closely related to Monoclonius, for in the text we find it separated from that genus b] 

 Diclonius and the three new species of that genus, then proposed by Cope. We might infer, 

 therefore, that at that time Cope considered Dysganus as more closely related to Diclonius 

 than to Monoclonius. Indeed, the only character mentioned by Professor Cope in his original 

 description of the genus which in the present writer's opinion might be considered as indicating 

 for this genus any relationships with the Ceratopsia is the indefinite statement that "the longi- 

 tudinal grooves in the anterior and posterior cement columns are probably occupied by the 

 borders of the apices of successional teeth," conditions similar to those which are known to 

 obtain in the Ceratopsia. 



In a critical note published by Professor Cope in the American Naturalist of June, 1890, 

 page 571, he would seem, however, to have considered Dysganus as pertaining to the 

 Ceratopsida?. For in referring to the "two-rooted teeth," described by Marsh as peculiar to 

 that family of dinosaurs, he remarks: 



The "two-rooted teeth," described by Professor Marsh * * * are not such in point of fact. The appearance of two 

 roots is produced by the absorption of the middle part of a single root by the crown of the successional young tooth. * * * 

 Teeth of this kind were figured by Leidy as belonging to Trachodon , and were described by me as representing the new genus 

 Dysganus. 



In his list of the species of the family Ceratopsidse (Agathaumidse), published on pages 

 715-717 of the American Naturalist for August, 1889, Cope makes no mention of the genus 

 Dysganus nor of any of its included species. 



Hay, in his Bibliography and Catalogue of the Fossil Vertebrata of North America, remarks 

 that it is a genus of uncertain affinities, though, as we have already remarked, he placed it in 

 the Trachodontida?, while Nopcsa has, as we have pointed out, referred it without question to 

 the Ceratopsida?. 



After a careful study of all the literature on the genus and its included species I am con- 

 vinced that the genus Dysganus was based on teeth pertaining to two or more genera 

 belonging in part to the Trachodontida? and in part to the Ceratopsida?. 



In view of this and the absence of the type specimens a and the imperfect nature of the 

 material upon which the genus was based, as well as the lack of any figures or sufficiently 

 exact description of the particular teeth, considered by Cope as the type of the genus, to fix 

 their true nature, I feel warranted in excluding it from the recognizable genera of the Cera- 

 topsida?. It should, I believe, be considered as a nomen nudum. 



MONOCLONIUS Cope. 1876. 



Type, species, M . crassus Cope. 



Original description in Proc. Acad. Nat. Sci. Phila., vol. 28, 1876, pp. 255-256. 



Cope, E. D., Bull. U. S. Geol. and Geog. Surv. Terr., vol. 3, 1877, p. 573; Proc. Acad. Nat. Sci. Phila., 1883, p. 99; Am. Nat- 

 uralist, vol. 23, 1889, pp. 715-717 and 906, and vol. 26, 1892, p. 757; Am. Geol., vol. 8, 1891, p. 56. 



Baur, G., Science, vol. 17, 1891, pp. 216-217; Am. Naturalist, vol. 24, 1890, p. 570; Am. Naturalist, vol. 25, 1891, pp. 448, 450. 



Dana, J. D., Manual of Geology, 1895, p. 847. 



Hatcher, J. B., Am. Naturalist, vol. 30, 1896, p. 113. 



Lambe, L. M., Cont,r. Canadian Pal., vol. 3 (quarto), pt. 2, 1902, pp. 9, 20, 21. 



Marsh, O. C, Am. Jour. Sci., 3d ser., vol. 41, Feb., 1891, p. 176; 3d ser., vol. 43, Jan., 1892, pp. 83-84; 3d ser., vol. 50, Dec, 

 1895, p. 497; Sixteenth Ann. Rept. U. S. Geol. Survey, pt. 1, 1896, pp. 217, 243. 



Nopcsa, F. Baron, Foldtani Kozlony, Budapest, 1901, vol. 31, p. 270. 



Woodward, A. S., Outlines of Vertebrate Palaeontology, p. 213. 



Zittel, K. A. von, Text-book of Palaeontology, English translation by C. R. Eastman, vol. 2, p. 245. 



The chief distinctive characters of this genus are its small size, the diminutive supraorbital 

 horn cores pointing directly upward; the short, broad, and widely fenestrated parietals; the 

 short squamosals, as indicated by the squamosal border on the parietals in the type. 



• a See footnote on p. 67. 



