80. STRUCTURE AND AFFINITIES OF THE BRONTOTHERID, 
Dinocerata of the Eocene,* which they seem to have replaced, they 
equalled them in size, and resembled- them in several important 
features, notably in the structure of the feet, and in having the 
head armed with a pair of powerful horns. The general structure 
of the group, however, clearly indicates that they do not belong 
in the order Dinocerata, but should be placed with the Perisso- 
dactyls, in which they form a well-marked family. 
The more prominent characters of this family were pointed out 
by the writer in describing Brontotherium gigas Marsh, the typ 
species, and others had been previously mentioned by Dr. Leidy. 
in his descriptions of Titanotherium Proutii.+ The skull of 
latter genus is not known, but there can now be no reasonab 
doubt that it was furnished with horns, in some respects similar 
to those of Brontotherium (plates i and ii). The possibility 
this was originally suggested by Dr. Leidy,t and in his latest wor 
he has figured a horn-core from the same deposits which yielde 
the Titanotherium remains. The fragmentary specimen 
scribed by Dr. Leidy as Meyacerops Coloradensis|| probably belongs 
in the same family, but until additional remains are found thi 
point cannot be decided. The supposed genera Symborodon and 
Miobasileus, recently indicated by Prof. Cope (vii, p. 723), bele 
to this group. The former is generically identical with Bron 
therium, the reputed absence of lower incisors being evidently d 
as shown below, either to age, or to imperfect specimens. 
basileus is apparently the same genus, and hence both nan 
should be regarded as synonyms of Brontotherium. ; 
Among the more marked characters of the Brontotheridæ, W 
readily distinguish them from the Rhinocerotide, apparently 
-~ near allies, may be mentioned the following :— There are 
Short and thick toes in the manus, and three in the pes. 
‘Skull supports a pair of large horn-cores, placed transversely, 
_ in modern Artiodactyls.€ There are well developed canine te 
_ in both jaws. The molar teeth, above and below, are not oft 
Rhinoceros type, but resemble those of Chalicotherium. 
* AMER. NAT., vol. vii, p. 146, March, 1873. 
Mammalia, p. 206, 1869. 
§ Extinct Vertebrate Fauna, pl. xxviii fig. 3, 1873 oe 
me Poi Se ; p , a 
l a Phil. Acad., 1870, p. i, and Extinct Vertebrate Fauna, p. 239. 
_ _ 1 Rhinoceros pleuroceros Duy., m the Miocene of France, has a transverse P 
_ Small horn-cores on the nasals, not unli je in Dinoceras, R. minutus 
