14 
MUSEUM BULLETIN NO. 12. 
As regards the supraorbital horn-core doubtfully assigned to 
M. crassus its similarity in form to that of Brachyceratops mon - 
tanensis, 1 Gilmore is noteworthy. This “striking similarity" 
has been remarked on by Gilmore (page 10) who suggests a 
possible identity with his genus. 
Owing to the imperfections of the parietals of M. crassus 
and the doubt regarding the proper association of the short 
brow-horn and the rest of the described material with this part 
of the frill, it is clear that the genus Monoclonius rests on an 
uncertain basis and is in need of further elucidation. 
If the main characters of the skull of Ceratops montanus 
and Monoclonius crassus are to be made known more compre- 
hensive material must be forthcoming, preferably from the Judith 
River district in Montana. The above two genera are, in the 
writer’s opinion, not sufficiently defined for use at the present 
time. In the case of Ceratops there is a paucity of material 
inadequate in full diagnostic characters. With Monoclonius 
its non-employment as a generic term is considered advisable 
on account of the composite nature of the material described 
which lacks data both as regards localities and the association 
of the skeletal elements in the field. 
Relying on the characters of the skull, the Homed-dinosaurs 
appear to fall into three natural groups or subfamilies which are 
derived through separate lines of descent from one or more 
ancestral forms still undiscovered. These three groups are as 
follows: (a) Eoceratops of the Belly River formation leading 
to the later Triceratops and Diceratops; (b) Centrosaurus, 
Styracosaurus, and Brachyceratops, an apparently natural group 
of which the members are all from the Belly River formation 
and have no known descendants; and (c) Chasmosaurus of the 
Belly River formation ancestral to Torosaurus. 
The main characteristics of the horn-cores and neck frill 
in these groups appear to be as follows : — 
1 Smithsonian Miscellaneous Collections, 1914, Vol. 63, No. 3; A new 
Ceratopsian Dinosaur from the Upper Cretaceous of Montana with note 
on Hypacrosaurus, pp. 1-10, Plates 1 and 2, and text figures. 
