Prof. 0. C. Marsh — Gigantic Ceratopsidce. 3 



on the median line. In old specimens, they are firmly coossified 

 with each other, and with the rostral bone. They send upward a 

 strong process to support the massive nasals. Another process, long 

 and slender, extends upward and backward, forming a suture with 

 the maxillary behind, and uniting in front with a descending branch 

 of the nasal. The premaxillaries are much excavated externally for 

 the narial aperture, and form its lower margin. They are entirely 

 edentulous. 



The maxillaries are thick, massive bones of moderate size, and 

 subtriangular in outline when seen from the side. Their front 

 margin is bounded mainly by the premaxillaries. They meet the 

 pre-frontal and lachrymal above, and also the jugal. The alveolar 

 border is narrow, and the teeth small, with only a single row in use 

 at the same time. The teeth resemble, in general form, those of 

 Hadrosaurus. 



The nasal bones are large and massive, and greatly thickened 

 anteriorly to support the nasal horn-core. In the skull figured on 

 Plate I. these bones are separate, but in older individuals, they 

 are firmly coossified with each other, and with the frontals. The 

 nasal horn-core ossifies from a separate centre, but in adult animals 

 it unites closely with the nasals, all traces of the connection being 

 lost. It varies much in form in different species. 



The frontals form the central region of the skull, and have been 

 greatly strengthened to support the enormous horn-cores which 

 tower above them. These elevations rest mainly on the frontal 

 bones, but the supra-orbitals, the post-orbitals, and the post-frontals, 

 have, apparently, all been absorbed by the frontals, to form the solid 

 foundation for the horn-cores. 



These horn-cores are hollow at the base, and in form, position, 

 and external texture, agree closely with the corresponding parts of 

 the Bovidce. They vary much in shape and size in different species. 

 They were evidently covered with massive pointed horns, forming 

 most powerful and effective weapons. 



The orbit is at the base of the horn-core, and is surrounded, 

 especially above, by a very thick margin. It is oval in outline, and 

 of moderate size. Its position and form are shown in Plate I. 

 Figure 1 b. 



The enormous posterior crest is formed mainly by the parietals, 

 which meet the frontals immediately behind the horn-cores. The 

 margin is protected by a series of special ossifications, which, in life, 

 had a thick horny covering. These peculiar ossicles, which extend 

 around the whole of the crest, may be called the epoccipital bones 

 (Plate I. Figures 1 and 2, e). In old animals, they are firmly 

 coossified with the bones on which they rest. 



The lateral portions of the crest are formed by the squamosals, 

 which meet the parietals in an open suture. Anteriorly, they join 

 the frontal elements which form the base of the horn-core, and 

 laterally, they unite with the jugal. The supra- temporal fossa? lie 

 between the squamosals and the parietals, as shown on Plate I. 

 Figure 2, c. 



