DAKOTA AND NEBRASKA. 



103 



ones, togetlier with the greater portion of a mutilated cranium, the fragment of a 

 lower jaw and the isolated unworn crown of a fourth upper premolar tooth, from 

 Eagle-nest Butte, between White River and the L'eau-qui-court, or Niobrara River, 

 appear to belong to 0. major. These specimens are more crushed than those from the 

 Mauvaises Terres of White River are usually, and are imbedded in a matrix of a 

 somewhat different color and texture. The former specimens, referred to 0. major, 

 are likevvi,se imbedded in a matrix slightly differing from that found attached 

 generally to the White River fossils, and approaching in appearance that of the last 

 mentioned specimens, from which circumstance I am led to suspect that O. major 

 belonged to a different stratum from 0. Calbertsoni and 0. gracilis. This may 

 account for the comparative rarity of ihe remains of the large species in the collec- 

 tions brought from tlie localities of the latter. 



In the upper jaw specimen above mentioned, from Eagle-nest Butte, the permanent 

 premolars had just assumed their functional position, and are therefore nearly 

 unworn. The teeth of this fossil are generally larger than those of the White River 

 skull. Their measurements are as follow : 



Length of the molar series, . 

 Length of the true molar series, 

 Length of the premolar series, 

 Antero-posterior diameter last molar, 

 Transverse " " 



Antero-posterior diameter second molar, 

 Transverse " " 



Antero-posterior diameter first molar. 

 Transverse " " 



Antero-posterior diameter last premolar, 

 Transverse " " 



Antero-posterior diameter third premolar, 

 Transverse " " 



Antero-posterior diameter second premolar. 

 Transverse " " 



Lines. 



50 

 27 

 26 

 11 

 10 

 10 

 10 



8 



8 



7 



8 



7 



6J 



7 



5 



A specimen in Dr. Hayden's collection of Mauvaises Tei*res fossils, of the expedi- 

 tion of 1866, consists of the mutilated flxcial portion of a skull, together with a small 

 fragment of the lower jaw. 



The bone is less hard and more chalky than in most of the other fossils with 

 which the specimen is accompanied, and the attached matrix is rather softer, more 

 ashen in hue and more homogeneous than that adhering to most of the fossils from 

 White River. 



