10 
MUSEUM BULLETIN NO. 12. 
As already stated this species was originally referred by 
the writer in 1902 to the genus Monoclonius, Cope. In 1907 
Mr. J. B. Hatcher, in his monograph on the Ceratopsia assigned 
it to Ceratops, Marsh. In the writer’s opinion neither of these 
genera is at present on a sound basis and available for use. 
The genus Ceratops, Marsh (type species C. montanus ) 
is Based on a pair of supraorbital horn-cores and an occipital 
condyle belonging to one individual from the Judith River 
beds on Cow creek, a tributary of Missouri river in Montana, 
U.S.A. No other parts of the skeleton are known. These 
horn-cores curve “strongly outward and slightly forward” 
(Ceratopsia monograph, page 172) the concave curve being on 
the outer side of the core. In Eoceratops the opposite is the 
case, the horn-core curving inward and backward with the 
concave curve on the inner side. 
The validity of the genus Ceratops rests mainly on the shape 
of a pair of supraorbital horn-cores, and if any reliance can be 
placed on the position, size, and shape of horn-cores in the Cera- 
topsidse as an aid to differentiation in that family then the 
supraorbital horn-cores of Eoceratops canadensis clearly indicate 
its distinctness from Ceratops, without reference to other parts 
of the skull which in the case of Ceratops are not at present 
available. Such a decided dissimilarity in the shape of the 
brow-horns suggests equally great differences, most probably 
of generic value, elsewhere in the skull. From our present 
knowledge of the horn-cores of the Ceratopsidae their curvature, 
or the direction of their growth, is constant in any species. 
In individuals of the same species there is remarkably little 
variation in the curvature or direction of growth of both the 
supraorbital and nasal horn-cores. This is seen in Styracosaurus, 
Centrosaurus, Eoceratops, Chasmosaurus, and Triceratops, 
and is probably true of all the genera. Differences of size occur, 
no doubt due to age and possibly to sex, but apparently the growth 
of a horn-core is in a definite direction, forward, upward, or back- 
ward, and also with inward or outward curvature in the case of 
brow-horns, according to the genus and species to which the in- 
dividual belongs. 
