O. C. Marsh on the Affinities of the Brontotheride. 83 
The mandible has a wide condyle, and a slender coronoid 
process. ‘The angle is rounded, and slightly produced down- 
ward. The symphysis is depressed, elongated, very shallow in 
front, and completely ossified. 
The dental formula of Brontotherium is as follows :— 
Incisors, >; canines, =} premolars, 2; molars, —x 2 = 38. 
The upper incisors are quite small. The canine is short and 
deeply concave, while the inner cones are low and separate. 
The lower incisors were small, and evidently of little use. The 
specimen in the Yale Museum has the crown hemispherical in 
form e lower incisors are not unfrequently wanting, and 
in old animals the alveoli may, perhaps, disappear. Careful 
examination, however, will usually show indications of them. 
€ lower canine is of moderate size, and separated from the 
premolars by a short diastema. The lower molars are of the 
Paleeotherium type, and agree essentially with those of Titano- 
therium. 
The head in Brontotherium was declined when in its natural 
Position. The neck was stout, and of moderate length. The 
cervical and most of the dorsal vertebre are distinctly opistho- 
ceelous. The latter are in general elevated. The atlas is large, 
and much expanded transversely. The axis is massive, an 
\ts anterior articular faces much broader than in the Dinocerata. 
The odontoid process was stout and conical. The transverse 
process was small, and apparently imperforate. _ posterior 
articular face is concave, and oblique. The epiphyses of the 
vertebrae are loosely united in most specimens, as in the Pro- 
boscidians. The caudal vertebree preserved indicate a long and 
tail. 
_ The limbs of the Brontotheride were intermediate in ae 
ros. The 
umerus is stout, and its entire distal end is A by the 
ridge similar to that of the Elephant, but not continued so far 
up the shaft. The ulna has its olecranon portion much com- 
pressed. Its distal end is much smaller than in Rhinoceros, and 
