MOLAR TEETH OF THE MAMiMALIA EDUCABILIA. 247 



molar series the flattening of the outer tubercles may proceed so 

 far as to produce, on wearing, a confluence of the [resulting] cres- 

 centoid surfaces. ... In both PalcBosyops and Hyrachyus these 

 tubercles of the upper molars are confluent into two Vs (more or 

 less open when unworn). In the former the inner tubercles retain 

 their primitive conic tubercular form, but in Palceotherium, Rhi- 

 nocerus, Lophiodon, Hyrachyus, and Tapirus they elongate trans- 

 versely so as to meet the corresponding outer tubercles (now crests) 

 forming the familiar cross-crests of those genera. If alternate, 

 the oblique crests of Palceotherium; if opjDosite, the cross-crests 

 of Tapirus. If, on the other hand, the inner tubercles flatten like 

 the outer, we have, on wearing, the quadricrescentoid [Selenodont] 

 type of the Euminatitia and Anoplotherium. In the Quadruma- 

 nous families, including man, the primitive quadrituberculate type 

 of molars is preserved." 



Four types of Lophodont dentition are included in the above 

 discussion, and three others may be added. They belong to two 

 series, viz., those in which the crests represent the modification 

 of opposite tubercles, and those where the tubercular elements of 

 the crown are alternate. These series may be called the Amoeho- 

 dont (alternate), and Antiodont (opposite), and the component 

 types are : 



Antiodonts. — Selenodont (Euminants) ; Tapirodont {Tapir, 

 Rhinocerus) ; Tricliecliodont (Manati, Elephant). 



Amcebodonts. — PalcBotheriodont (Palaeotherium, etc.) ; 8ym- 

 horodont (Palaeosyops Symborodon, etc.) ; Bathmodont (Bathmo- 

 don, etc.) ; Loxolophodont (Uintatherium, etc.). 



These types are defined as follows : 



1. Antiodonts. 



Selenodonts. — The tubercles separate or united at their angles, 

 much elevated, narrow crescentic in section, separated by deejj 

 valleys. 



To this group belong the molars of the Euminants, the Tra- 

 gulidm, the Oreodontidm, and MerycopotamidcB ; of Perissodac- 

 tyles the Equidm. 



Tapirodonts. — The outer tubercles longitudinally compressed, 

 subcrcscentic in section ; the inner transversely compressed, con- 

 tinued as transverse ridges to the end or middle of the correspond- 

 ing exterior crests. 



Rhinocerus, Tapirus, Hyrachyus, Lophiodon, and Hyrax rep- 



