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to 
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io 2) 
The American Naturalist. [March, 
Oreodon Beds. 
Reddish brown clays, with occasional concretionary layers, 
Remains of Oreodon, Hyracodon, Hyzenodon, Elotherium, etc. 
About 500 feet thick. 
Upper Beds, 30 ft. 
_ Characterized by Titanotheriidz of large size. Horns 10- 
18 in. long, elliptical to sub-ovate in cross-section. Nasals 
very short and pointed. Incisors never more than 2. Inter- 
nal cingulum on upper premolars not strongly marked in 
either sex. Posterior inner cone on last upper molar. Third 
trochanter present. Trapezium absent. General form of 
skull shown in fig. 1. 
Middle Beds, 100 ft. 
Characterized by Titanotheriidz of medium size. Horns 
4-10 in. long, circular to sub-triangular in cross-section. — 
Nasals of moderate length, with broad or pointed extremi- 
ties. Incisors never more than 2, Sfrong internal cingulum 
on upper premolars of males only. Posterior inner cone on 
last upper molar. Third trochanter present. Trapezium 
absent. General form of skull represented in fig. 2. 
TITANOTHERIUM BEDS, 180 FEET THICK. 
_ Lower Beds, 50 ft. 
Characterized by Titanotheriide of small size. Horns 
rudimentary or from 1-4 in. long, circular in cross-section 
Nasals long and pointed. Incisors occasionally as many aS 
3. Strong internal cingulum on upper premolars in males 
only. No posterior inner cone on last upper molar. Third 
trochanter somewhat rudimentary. Trapezium present in 
earliest forms. General form of skull shown in fig. 3. 
Underlying 
Represented by various formations from Laramie to Archean. 
Section of Titanotherium Beds showing relative thickness of Upper, Middle, and 
Lower Beds, with brief descriptions of forms of Titanotheriidee common to 
