104 Bulletin American Museum of Natural History. [Vol. XVI, 



Two skulls in the National Museum (Nos. 47 ii, 4705) ex- 

 hibit smaller canines than in Marsh's type, and possibly repre- 

 sent a fourth species, 

 jj r iM because the canines are 



exceptionally small, the 

 nasals excessively thin, 

 the horns elongate, set 

 wide apart and very far 

 back, oval in section at 

 the top. 



Phylum IV. 



Titanotheres attaining 

 the largest size, with vertex 

 of cranium greatly elong- 

 ated by extension of horns 

 in front of orbit and of 

 occiput behind zygomata. 

 Skull, hoivever, as meas- 

 ured along the basal line 

 and across the zygomata progressively brachycephalic. Horns 

 transverse oval in section from base to summit, shifting for- 

 ward and progressively elongating and flattening. Nasals 

 abbreviating. Incisors |-. Canines stout, blunt, obtuse. Pre- 

 molars 7^, cins'uluiii des'eneratin^. 



4-3 ' t5 c> C5 



Fig 8 Sy>nbotodon > montaniis (Marsh). 

 Nat. Mus. No. 4711, Sk. V.) 



Genus BRONTOTHERIUM Marsh. 



Syn., Titanops Marsh. 



The type of this genus is the Brontothcrium gigas jaw 

 (Yale Museum), with which the type jaw of Titanops elatus 

 (Yale Museum) is practically identical. The succeeding 

 species {B. curium, B. ramosum, B. dolichoceras , B. platy- 

 ceras) of very long, flat-horned Titanotheres therefore belong 

 to Brontothcrium. 



A discovery of great interest is a very primitive skull of 



