148 FOSSIL MAMMALS OF THE ORDER DINOCERATA. 
certainty the nature and affinities of this most singular group of 
animals, and the more important characters are here mentioned, 
preliminary to the full description. Most of the cranial characters 
are derived froma very perfect skull of Dinoceras mirabilis, figured 
in the accompanying plates. 
The skull is unusually long and narrow. The three pairs of horn- 
cores, rising successively above each other, and the huge crest 
around the. deep concavity of the crown, together with the large 
decurved trenchant tusks, unite in giving a most remarkable ap- 
pearance to the’ entire head (Plates I, IL), which differs widely from 
anything known among living or fossil forms. 
The structure of the skull. presents many features of interest. 
The supraoccipital is greatly developed, and, after rising above the 
brain-case, forms an enormous crest, which projects obliquely back- 
ward beyond the condyles. This crest is continued forward on 
either side, each lateral portion sloping outward, and overhanging 
. the large temporal fossa. This portion of the crest is formed 
largely of the parietals. The posterior pair of horns rise from 
this crest, which is thickened below on the inner side to support 
them. In front of these horns, the crest descends rapidly, and 
subsides nearly over the centre of the orbit. These posterior 
horn-cores are higher than those in front, and have obtuse summits, 
flattened transversely. (Plates I, II.) The frontal bones have no 
postorbital process, and the orbit is not separated from the tem- 
poral fossa. The latter is very large posteriorly. (Pl. II, fig. 1.) 
The squamosal forms the lower portion of the temporal fossa, and 
sends down a massive post-glenoid process. It likewise sends 
forward a zygomatic process, which resembles that of the tapir. ` 
The malar completes the anterior portion of the arch, which is not 
the case with any known Proboscidian. The lachrymal is large, 
and forms the anterior border of the orbit, as in the rhinoceros. 
It is perforated by a large foramen on its facial surface. Over the 
orbit, the frontal sends out laterally a prominent ridge, which 
afforded good protection to the eye in the combats of these ani- 
mals with each other. On this ridge there is a small protuberance, 
which closely resembles a diminutive hosn-core, but its position, 
immediately i in front of the lateral crest, renders it probable that 
it did not support a true horn. 
The maxillaries are massive, and quite remarkable in supporting 
à pair of e conical horn-cores, The bases of these cores 
he 
