MONOCLON1US RECURVICORNIS 83 



Monoclonius recurvicornis Cope 10 



Holotypc: No. 3°' il1 A.M.N.H.; upper portion of facial region bearing both supraorbital and nasal horns, 

 together with a fragment of the left jug.il, and part of the margin of the right squamosal with two epoccipitals. 

 Horizon: Judith River formation. 

 Locality: The same as M. crassm. 

 Collector: E. D. Cope and party, 1876. 



Except for the supraorbital horn of M. crassus, which does not belong to the holotype, there 

 are no parts of the skulls of M. crassus and M. recurvicornis preserved which are homologous and 

 therefore, comparable. Hence, specific distinction is not demonstrable. 



There is a skull of Monoclonius {Centrosaurus) in Ottawa (No. 348 G.S.C.) in which the nasal 

 horn is quite similar to that of Cope's type in the degree of its forward curvature. The left brow 

 horn is relatively nearly as large as in recurvicornis, but the right is much smaller, nor have either of 

 them the same form as in recurvicornis. There the resemblance ceases, as the Ottawa specimen 

 shows no trace of a small horn-like prominence borne on the prefrontal on either side about midway 

 between the nasal and brow horns. Beyond this, comparison cannot be made. 



Monoclonius sphenocerus Cope 11 



Holotype: No. 3989 A.M.N.H.; nasal horn, nasal and left premaxillary. 



Horizon: Judith River formation. 



Locality: On Missouri River, near Cow Island. 



Collector: C. H. Sternberg, 1876. 



Here, again, no comparison can be made with homologous elements in M. crassus. This is not 

 true, however, of M. recurvicornis and M. sphenocerus, for in each instance the nasal horn is present. 

 The two horns are very different in character, that of the species under discussion being straight, erect, 

 laterally compressed, and of great fore and aft diameter at the base, with a rapid diminution of this 

 dimension toward the tip. In recurvicornis, on the other hand, the basal section is more broadly 

 elliptical and the horn curves sharply forward. Clearly, therefore, M. recurvicornis and M. spheno- 

 cerus are specifically distinct, but, unfortunately, neither species can be differentiated from M. crassus, 

 the type of the genus, which, in case of proved identity, would take precedence over either recurvi- 

 cornis or sphenocerus, but which one cannot say. So here the matter rests until more adequate 

 material is secured from the Judith River formation. 



The comparison between the M. sphenocerus horn and that of Styracosaurus albertensis will 

 shortly be discussed and the relationship between them, which some have argued, dismissed as 

 unproved. 



(?) Monoclonius dawsoni Lambe 12 



Holotype: No. 1173 G.S.C; parts of two skulls. 



Horizon: Belly River formation. 



Locality: Red Deer River, between Berry Creek and Dead Lodge Canyon, Alberta. 



Collector: L. M. Lambe, 1901. 



Mr. Lambe's description is as follows: "The remains of an apparently undescribed species of 

 this genus, consisting of the skull of one individual and the posterior crest of another, are of especial 

 interest. The skull when found lay on its right side and although very much crushed, certain 

 parts of it supply definite information as to its structure and size. The two orbits, the right maxilla, 

 a quadrate, and the occipital condyle were conspicuous and apparently in place, with a large posterior 



10 Cope, E. D., 1889, p. 716. 



11 Cope, E. D., 1889, pp. 716-717. 



12 Lambe, L. M., 1902, pp. 57-63. 



