PLATE CLXXXVI 



Skulls of Beontotheeium and Megaceeops 

 Plate prepared under the direction of Professor Marsh. One-sixth natural size. (See p. 575) 



A, Brontotherium curtum, type (Yale Mus. 12013), Colorado, Chadron formation, upper levels. Front view. Type of Tiianops 



curtus Marsh. The long horns in this highly speciaUzed brontothere are much flattened in cross section and much larger than 

 in the type of B. platyceras. The incisors are not preserved. 



B, Skull referred to Megacerops? sp. (Nat. Mus. 1220?). This skull appears to be allied to Megacerops tonus or M. acer. As in 



that genus, the nasals are short and thick, the horns elongate, slender, the zygomata massive and thick vertically. The 

 presence of two incisors does not definitely exclude this specimen from Megacerops, because the type of M. acer retains alveoli 

 for two small incisors. 



C, Type skuU of Brontotherium dolichoceras (Harvard Mus.), South Dakota, Chadron formation. In this specimen the horns are 



more slender and less widened transversely than in other brontotheres. They are suboval at the base. In Megacerops a 

 connecting crest is usually lacking and the horns are thicker at the base. 



