164 0. a Marsh— Principal Characters of the 



the genus there is a prominence on the frontal, directly over 

 the orbit. The nasals are greatly elongated, being nearly half 

 the length of the entire skull They unite with the frontals 

 by oblique sutures, directed backward and inward, and nearly 

 parallel with the superior fronto-parietal sutures. (Plate II, 

 figure 3.) The osseous protuberances on the extremities of 

 the nasals are of moderate size in Dinoceras, but, like the max- 

 illary horn-cores, vary much with age. Both may possibly 

 have been covered with thick skin, and not with true horns. 



The orbit is large, and confluent with the temporal fossa. 

 The latter is of great extent posteriorly, but the zygomatic arches 

 are only moderately expanded. The squamosal forms the 

 lower portion of the temporal fossa, and sends down a massive 

 post-glenoid process, which bounds in front the external audi- 

 tory meatus. The latter has for its posterior border the post- 

 tympanic process of the squamosal, which unites directly with 

 the paroccipital, thus excluding the mastoid from the external 

 surface of the skull, as in Rhinoceros. The tympanic portion of 

 the periotic, also, does not reach this surface. There are small 

 air-cells in the walls of the temporal fossa, both in the squamo- 

 sal and parietals. The squamosal sends forward a strong zygo- 

 matic process, which resembles that in Tajpirus. The malar 

 completes the anterior portion of the arch, extending to the 

 front of the orbit. (Plate II, figure 1.) The lachrymal is large, 

 and forms the anterior border of the orbit. It is perforated by 

 a large foramen. The maxillaries are massive, and quite re- 

 markable in supporting a pair of stout, conical horn-cores, 

 which vary in form and size in different species. These cones 

 are solid except at the base, which is usually perforated for the 

 fang of the canine tusk. The premaxillaries are elongated, and 

 without teeth. They unite posteriorly with the maxillaries just 

 in front of the canine, and then divide, sending forward two 

 branches, which partially enclose above and below the lateral 

 portion of the narial aperture. (Plate II, figure 1.) The lower 

 portion is slender, and resembles the premaxillary of some 

 Ruminants. The premaxillaries are not united at their ex- 

 tremities. The latter are rough, and probably supported a pad. 



The palate is very narrow and deeply excavated, especially 

 in front. The anterior palatine foramina are in the premaxilla- 

 ries, and vary much in different species. In D. mirahiU they 

 are elongated fissures, enclosed between the lateral and palatine 

 branches of the premaxillaries, as in Equus. In D. laticeps they 

 are of small size, and oval in outline. The posterior palatine 

 foramina are in the maxillaries near the anterior border, as in 

 Hi2>popotamus. The posterior nares extend forward between 

 the last upper molars. The occipital condvles are large, and 

 bounded extenially in front and below by a "deep groove.^ They 



