86 



THE CEEATOPSIA. 



to a young individual. In this respect this element resembles very closety the same portion of 

 the squamosal in Marsh's type of Sterrholoplms flabellatus, founded on a very complete skull 

 of a young individual, and I am inclined to the opinion that the smooth surface of the squamosals 

 and parietals upon which Marsh largely based his generic distinctions was due rather to the 

 immature age of the individual than to generic differences. 



The supraorbital horns in the type of the present species appear to be attached by suture 

 to their supporting elements and to have been developed from distinct and separate centers of 



ossification, much as the horn 

 cores in the giraffe. In other 

 words, they seem to have an origin 

 independent of the other elements 

 of the skull, which serve them 

 simply as supports. In each 

 supraorbital horn core in the 

 present instance there appears 

 at the base a distinct ridge, well 

 shown in the accompanying fig- 

 ures, entirely encircling the base 

 of the horn and giving the appear- 

 ance of a suture which has not yet 

 been fully obliterated, owing, per- 

 haps, to the somewhat immature 

 age of the individual. This lat- 

 ter condition is further indicated 

 by the somewhat imperfect union 

 of the epoccipitals already re- 

 ferred to. Certain characters just 

 referred to in the present skull 

 would seem to suggest that the 

 supraorbital horn cores in the 

 earlier Ceratopsia at least were 

 developed independently of the 

 other cranial elements, while the 

 nasal horn was derived in part 

 also from a distinct center of 

 ossification. 



The material above described, 

 which forms the type of the pres- 

 ent species, represents an ani- 

 mal of considerable dimensions. 

 Though smaller than any of 

 the Ceratopsia from the Lara- 

 mie of Wyoming, Montana, or 

 Colorado, it was nevertheless 

 decidedly larger than most of 

 those known from the Judith River beds. In the development of the supraorbital horn 

 cores it shows a very decided advance over M. crassus, the type species of the genus, provided 

 the supraorbital horn referred to by Cope really pertained to that species. The fragment of 

 squamosal preserved also shows a very marked modification in the direction shown in the genera 

 Ceratops, Triceratops, and Sterrholophus of Marsh. It is so different and distinct from that 

 of the type species of the genus M. crassus that when it is considered in connection with the 

 other structural differences found in other portions of the skull, more especially the horn cores, 

 I do not hesitate to refer it to a distinct genus, Ceratops of Marsh, founded on very similar 



Fig. 90.— A, Lateral view of type of Monoclonius recurvicornis Cope, No. 3999, American 

 Museum of Natural History; B, front view of same; C, top view of nasal horn of 

 same, was, Nasal; nh, nasal horn core; o, orbit; soh, supraorbital horn core. All one- 

 sixth natural size. After Cope.o 



a From Am. Naturalist, vol. 23, PI. XXXIV. 



