918 



EOCENE AND OLIGOCENE TITANOTHERES OF MONGOLIA 



Distinctive characters oj jour genera of titanotJieres 



Note. — The single lower molar of a species of MenoditSj discovered in the Erontops j 

 which the name Menodus mongoUensis has been assigned. 



DESCRIPTIONS OF SPECIES 



SUBFAMILY DOLICHORHININAE 

 Dolichorhinus Hatcher, 1895 



The generic characters of this long-nosed titano- 

 there as it lived in Mongolia are readily determined by 

 comparing the single type jaw of DolichorJiinus olseni, 

 from the Irdin Manha formation, with the three excep- 

 tionally well-preserved skulls and jaws of DolicTiorJiinus 

 Tcaiseni, including also palate and basicranium with 

 complete dentition, from the overlying Shara Murun 

 formation. The genus is named from its long, narrow, 

 transversely arched nasals, which descend in sharp, 

 broad plates at the sides. No other titanothere 

 exhibits this feature. The cranial proportions are 

 correspondingly elongate, laterally compressed, arched 

 superiorly with slender, flattened zygomatic arches 

 correlated with relatively feeble powers of mastica- 

 tion; the breadth-length index, 47 (length 695 mm., 

 breadth 330 mm.), contrasts with an index of 69 in a 



lieiisis zone, represents a much larger animal— long-headed, narrow-toothed — to 



skull of Protitanotherium grangeri of the same basilar 

 length, namely, 695 millimeters. The horns are not 

 elongate but are rounded, short, obtuse, and much 

 more prominent than in any known American species. 

 The jaws are elongate, slender, angulate, with slender 

 coronoid processes. The dentition harmonizes with 

 the relatively feeble masticating and offensive powers, 

 the canines being relatively small, the incisors of me- 

 dium size with posterior cingula, the second lower 

 incisors slightly enlarged. In these, as in the Amer- 

 ican species, the premolars are simple and have large 

 median internal deuterocones and rudimentary tetarto- 

 cones. 



In the Irdin Manha formation occurs the more 

 primitive species Dolichorhinus olseni, represented by 

 a beautifully preserved type jaw, and in the Shara 

 Murun formation occurs the more progressive species 

 Dolichorhinus Icaiseni, represented by three skulls and 

 jaws and one complete palate and basicranium, as 

 enumerated in the tables given above. 



