EOCENE AND OLIGOCENE TITANOTHERES OF MONGOLIA 



931 



to those in P. mongoliense and P. grangeri; (4) the 

 superior and inferior canines, however, of the males 

 appear to be larger and more robust at the base, 

 not obtuse toward the summit, less lanceolate, more 

 recurved, than in the male canines of P. grangeri; (5) 

 the superior incisors exhibit a distinct feature in the 

 relative reduction in size of the lateral incisors, i^, 



sculpturing of the inferior premolars and molars is very 

 marked; the cingulum stands out promiuently in the 

 premolars and very prominently in the molars, espe- 

 cially in mg (Am. Mus. 20272, referred; 20271, type); 

 this cingulum prominence distinguishes P. andrewsi 

 from its ancestor P. mongoliense of the Shara Murun 

 and very distinctly from the more ancient P. grangeri. 



Figure 787. — Type cranium of Proiitanotherium andrewsi Osborn (Am. Mus. 20271), Shara Murun 



formation 



One-sixth natural size. This large male cranium lacks the anterior frontonasal region. The large canines are thoroughly characteristic 

 of the species. Observe the distinct development of the tetartocones in p^, also the small hypocones in m3. 



and in the bluntly rounded summits of the second 

 incisor, i^ (Am. Mus. 20271), which are similar to 

 those in P. mongoliense; (6) the inferior incisors (Am. 

 Mus. 20269) lack this rounded obtuse character of 

 the summits and preserve the pointed postcingulate 

 ■character seen in P. mongoliense. 



The inferior premolars (Am. Mus. 20271, type; 

 20272, referred) present a slight but distinct progres- 

 sion of the entoconids, metastylids, and valleys of the 

 talonid upon the P. mongoliense stage. The external 



Skeletal remains referred to Protitanotherium grangeri, 

 P. mongoliense, and P. andrewsi 



Skeletal material is rare in the Irdin Manha forma- 

 tion, but we may with some confidence refer to Proti- 

 tanotherium grangeri (Am. Mus. 20171, belonging to 

 more than one individual) portions of the right and 

 left fore limbs including both the ulno-radii, one 

 humerus, one tibia, and an axis, which display the 

 measurements shown on page 932 in comparison with 

 referred P. mongoliense and P. andrewsi. 



