100 Prof. O. C. Marsh—Restoration of Brontops. 
The skeleton represented in this restoration is by far the most 
complete of any of the group yet discovered. It was found by the 
author in Dakota, in 1874, and portions of it have been exhumed 
_at different times since, some of the feet bones having been recovered 
during the past year. It is a typical example of the family, and 
shows well the characteristic features of the genus and species which 
it represents. 
The most striking feature of the restoration here given, aside from 
the great size of the animal, is the skull. This is surmounted in 
front by a pair of massive prominences, or horn-cores, which are 
situated mainly on the frontal bones. The nasals contribute some- 
what to their base, in front, and the maxillaries support the outer 
face. These elevations, or horn-cores, vary much in size and shape 
in the different genera and species. They are always very small in 
the females. 
The general form of the skull and lower jaw is well shown in the 
figure. The prominent occipital crest, the widely-expanded zygo- 
matic arches, and the projecting angle of the lower jaw, are all 
characteristic features. In general shape, the skull resembles that 
of Brontotherium, but may be readily distinguished from it by the 
dental formula, which is as follows :— 
Incisors 2; canines +; premolars ¢ +; molars 3. 
The presence of four premolars in each ramus of the lower jaw is 
a distinctive feature in this genus. This character, with the single, 
well-developed lower incisor, marks both the known species. 
The number of teeth varies in the different genera. » The form of 
the teeth, especially in the molar series, is more like \ ‘hat in Chali- 
cotherium and Diplacodon than in any ‘other known forms. The 
teeth in the allied genus Brontotherium have already been figured 
and described by the author. 
The vertebree are somewhat similar to those of the existing 
Rhinoceros. In the present genus, Brontops, the neural spines of 
the dorsal vertebrz are elevated and massive. There are four sacral 
vertebree in this genus, and in the known species the tail is short 
and slender, as in the individual here described. 
The ribs are strong and massive. The sternal bones are com- 
pressed transversely. The exact form of the first one is not known 
with certainty, and is here restored from the Rhinoceros. This is 
the only important point left undetermined in the restoration. 
The fore limbs are especially robust. The humerus has its tuber- 
osities and ridges very strongly developed, and the radius and ulna 
have their axes nearly parallel. There are four well-developed 
digits in the manus, the first being entirely wanting. 
The pelvis is very wide and transversely expanded, as in the 
Hlephant. The femur is long, and has the third trochanter rudi- 
mentary. The tibia and fibula are quite short. The calcaneum is 
very long, and the astragalus is grooved above. There are only 
three digits i in the pes, the first and fifth having entirely disappeared. 
Diplacodon of the Upper Eocene is clearly an immediate ancestor 
of the Brontotheride, while Palgosyops and Limnohyus of the Middle 
