TYPES OF MOLAR TEETH OF MAMMALIA EDUCABILIA. T5 



Symborodonts. 



External tubercles longitudinally compressed and subcrescentic in section ; the 

 inner independent and unaltered, i. e. conic. 



To this group are to be referred the types of Palmsyops, Titanotherium, and 

 Symhorodon. They, of all Lophodonts, approach nearest to the Bunodonts. 



Bathmodonts. 



The posterior pair of tubercles approximated and connected, together com- 

 pressed and subcrescentoid in section ; the anterior outer connected with the ante- 

 rior inner by an oblique crest forming a V with the preceding. 



Bathmodon and Metalophodon. The homologies of the crests are difficult to 

 make out ; the subcrescentic crest may include only the posterior outer tubercle 

 and thus be entirely homologous with the posterior crescent of Palseosyops. In 

 support of this view we have the structure of the premolars where it becomes the 

 only external crescent, while the anterior transverse crest turns round on its inner 

 side, supporting the inner anterior tubercle of the tooth. But the fact that there 

 are two crests on it in the true molars, that one of these is near the position of the 

 inner anterior tubercle, and the fact that there is no other posterior tubercle, render 

 it probable that the homologies expressed in the above diagnosis are correct. 



Loxolophodonts. 



Anterior inner tubercle connected with the two external by oblique crests ; the 

 posterior inner tubercle rudimental or wanting. 



TJintatherium and probably Tillotherium represent this group, both being like 

 those of the last, extinct genera from the Eocene of Wyoming. 



2. The Mandibular Teeth. 

 The types of structure are less numerous than those of the maxillary teeth, 

 since I am only acquainted with six. Still more distinctly than those of the upper 

 jaw, do they represent the types of opposite or alternating tubercles, or the antio- 

 dont and amoebodont. The essential principles of modification are the same as in 

 the maxillaries, and they correspond with them as to genera, as follows : — 



Antiodont. 



Inferior. Superior. 



Selenodont. Selenodont. 



Hyracodont. Tapirodont pt. 



Trichecodont. 



Tapirodont pt. 

 Trichecodont. 



