O. C. Marsh—New Tertiary Mammals. 245 
metacarpal, and hence the line of descent for the four-toed forms 
was probably a different one 
Brontotheride. 
During a recent expedition to the ‘“‘Bad Lands” of Dakota, 
the writer secured a large number of ee preg to 
the Brontotheride, most of them in good preservation. From 
the Miocene of Colorado, explored by the writer in 1870, and 
subsequently, a large amount of similar material has been ob- 
tained, so that at the present time the Yale Museum contains 
portions of more than 100 different individuals of this family. 
study of these specimens, in connection with the types orig- 
inally discribed, promises to leave but few points in doubt in 
regard to the structure or affinities of the group. The results 
will be published at an early day, but a few are given here, 
which may clear up some of the existing confusion about the 
different genera 
It may now be regarded as established that all the species of 
the Brontotheride had horns, and there is no reasonable doubt 
that these were common to both sexes. The osseous horn-cores 
in each species varied much in size and shape with difference of 
age, and probably of sex. The incisors are small, and in old 
specimens are frequently lost 
here appear to be four well marked genera in Ree family 
now known, which may be distinguished as follow 
1. Titanotherium Leidy (Menodus Pomel.) 
Dentition =Incisors : canines = premolars = re molars - 
Diastema behind upper canines. Basal ridge on inner side of 
upper premolars not continuous. Nasals short. A postorbital 
process. Third trochanter rudimentary or wanting. ‘T'ype 7. 
Proutit Leidy. 
2. rele Leidy. (Megaceratops Cope), (Symborodon — 
n part.) 
2 ; 1 
Dentition =Incisors —; canines <1 premolars — ; molars ® . 
0’ 3 
Diastema behind upper canine. Inner basal ridge on upper 
premolars not continuous. Nasals more elongated. postor- 
bital process. Third trochanter rudimentary or wanting. Type 
Megacerops coloradensis Leidy. 
3. Brontotherium Marsh. (Symborodon Cope, in part.) (Aio- 
basileus Co ope.) 
: 2 ; 1 + 3 
Dentition =Incisors i canines +; premolars = ; molars = 
No superior diastema, Strong continuous basal ridge on inner 
