MOLAR TEETH OF THE MAMMALIA EDUCABILIA. 249 



• 2. Tlie 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 antiodont and amoebo- 

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

 the maxillaries, and they correspond with them as to genera, as 

 follows : 



Aktiodont. 



Inferior. 



Selenodont. 

 Hyracodont. 



Trichecodont. 



Superior. 



Selenodont. 



Tapirodont pt. 

 j Tapirodont pt. 

 ( Trichecodont. 



Amcebodoxt. 



J Palaeotheriodont. 



■ I Symborodont. 



Selenodont pt. 



j Bathmodont. 



( Loxolophodont. 



The characteristics of these groups are as follows : 



A. Antiodonts. 



Symborodont. 



Hippodont. 



Loxolophodont. 



Selenodonts. — Constructed, typically, like the upper molars, 

 Rummantia. 



Hyracodonts, — External tubercles compressed longitudinally 

 and crescentic in section, continuous by a cross-crest with the cor- 

 responding tubercle of the iuner side. 



The animals which possess this type of teeth are the Bliinoce- 

 riiSj Hyracodon, and the Hyrax ; it is nearly approached by some 

 of the Hyrachyi. It corresponds in structure with the true tapiro- 

 dont arrangement of the maxillary teeth ; but many of the Ta^^iro- 

 donts have the Trichecodont type of mandibular teeth. 



Trichecodonts. — Definition the same as for the maxillary teeth. 



Tapirus, LopModo7i, Hyracliyus, Dinotlierium, Eleplias, Tri- 

 checus (the manati), and the Kangaroos and their extinct allies 



belong here. 



B. Amcebodonts. 



Hippodonts. — In the horses the maxillary molars are con- 

 structed on an opposite crested basis, while the mandibulars repre- 



