PLATE CLXX 



Front View of Skulls of Three Brontotheres 

 Plate prepared under the direction of Professor Marsh. One-sixth natural size. (See pp. 562, 563, 668) 



A, Skull referred to Brontolherium hypoceras? (Nat. Mus. 4702), skull K', South Dakota, doubtfully recorded from the lower part 



of the Tiianotherium zone (Hatcher). This skull has small slender horns, but the grinding teeth are as large as in certain skulls 

 referred to B. gigas. The width across the zygomata is probably increased by flattening. 



B, Skull referred to Brontolherium hatcheri (Nat. Mus. 4255), skull Qi, South Dakota, Tiianotherium zone, level upper B (Hatcher), 



middle part of Titanotherium zone. The horns are a little longer than in the type of B. hatcheri but considerably shorter and 

 less flattened than in the typical B. gigas. The zygomata are not shown. 



C, Skull referred to Brontotherium gigas (Yale Mus. 12061; type skull of Titanops elatus Marsh), South Dakota, exact locality not 



published, Chadron formation. The horns are long and the nasals narrow. This stage is characteristic of the upper part of 

 the Tiianotherium zone (Hatcher). 



