194 Prof. 0. C. Marsh — Gigantic Ceratopsidce. 



are likewise entombed in this formation. Invertebrate fossils and 

 plants are not uncommon in the same horizon. 



The Skull of one species was described and illustrated in the 

 Geological Magazine for 1890 (Dec. III. Vol. VII. PI. I. pp. 1-5), 

 to which it will be sufficient to refer the reader. But the following 

 notes, supplementary thereto, form part of the paper which ap- 

 peared in the "American Journal of Science" for February, 1891. 

 Additional figures of the skull have since been prepared and are 

 given in Plates ^ IV. and V. 



In the figures of Triceraiops flabellatus (see Geol. Mag. 1890, 

 PI. I. Figs. 1, 2), it was pointed out that the rostral bone was free 

 and was not secured [op. cit. p. 2), but, in another skull, represented 

 in PI. IV. Figs. 2, 3, 4, and 5, the rostral bone and nasal horn-core 

 are in position, and firmly coossified with the adjoining elements. 



The frontal bones are quite short, and early unite with each other 

 and with the adjoining elements, especially those behind them. 

 The frontal or central region of the skull is thus greatly strengthened 

 to support the enormous horn-cores which tower above. These 

 elevations rest mainly on the post-frontal bones, but the supra- 

 orbitals and the post-orbitals are also absorbed to form a solid 

 foundation for the horn-cores. These horn-cores are hollow at the 

 base (see PL V. Fig. 1), and in general form, position, and external 

 texture agree with the corresponding parts of the Bovidce. 



The post-frontal bones are very large, and meet each other on the 

 median line. Posteriorly they join the squamosals and the parietals. 

 At their union with the latter there is a median foramen. (PI. V. 

 Fig. l,a;), which apparently corresponds to the so-called "parietal 

 foramen." ^ 



In old individuals it is nearly or quite closed. When open, it 

 leads into a large sinus, extending above the brain-case into the 

 cavities of the horn-cores. This foramen has not before been 

 observed in Dinosaurs. 



The palatine bones are much smaller than the pterygoids. They 

 are vertical, curved plates, outside and in front of the pterygoids, 

 and uniting firmly with the maxillaries. The vomers join the 

 pterygoids in front, where they appear as thin bones, closely applied 

 to eaclx other. 



The transverse bones give some support to the maxillaries, which 

 are further strengthened by close union with the pterygoids. They 

 meet the pterygoids behind, and the palatines in front. 



The Brain. — The brain of Triceratops appears to have been 

 smaller in proportion to the entire skull than in any known 

 Vertebrate. 



The position of the brain in the skull does not correspond to the 

 axis of the latter, the front being elevated at an angle of about 

 thirty degrees (Plate V. Fig. 2). 



1 Plate IV. appeared in the April Number, 1891 ; Plate V. is in the present 

 Number. 



* The name usually applied to this aperture is misleading, as in Chameleo and 

 some other reptiles the foramen is not in or near the parietal bones. It may more 

 properly be called the "pineal foramen." 



