PLIOLOPHUS. 



361 



the full complement ; thus in the Hyrax (fig. 122) the canines 

 are wanting, and there is but one incisor (i), which, however, 

 is of large size in each 

 premaxillary. In the 

 elephants the incisor be- 

 comes a tusk (fig. 147) ; 

 in the Eodents (fig. 1 65, i) 

 it acts as a chisel; in 

 the tapir the first pre- 

 molar is wanting (fig. 

 Ill), and other modifi- 

 cations, chiefly by defect 

 of number, are manifold among existing species. But in the 

 earliest known placental mammals the type-dentition, as for- 

 mulised in Pliolophus, was the rule, and has been manifested 

 in the following : — 



Fig. 122. 



Deciduous and permanent dentition, upper 

 jaw, Hyrax. 



FORMATIONS. 



Palceocyon 



Coryphodon 



Pachynolophus 



Lophiotherium 



Pliolophus 



Hyracotherium 



Palceotheriwm . 



Anoplotherium 



Anchitherium . 



Dichobune 



Xiphodon 



Dichodon 



Microtherium . 



Amphitragulus 



Amphimeryx . 



Dorcatherium . 



Chalicotherium 



Aplielotherium 



Anthracotherium 



Hyopotamus 



Sables de Braclieux (or somewhat older). 



Plastic clay. 



Calcaire grossier moyen. 



Marries lacustres d'Alais (Gard). 



London clay. 



London clay. 



Paris gyps. 



Paris gyps. 



Lignites de la Debruge, pres Apt. 



Binstead. 



Lignites de la Debruge. 



Hordwell. 



Marnes calcaires lacustres, Puy du Dome. 



Marnes lacustres en Velay. 



Lignites de Debruge. 



Miocene d'Eppelsheim. 



Miocene d'Eppelsheim. 



Marnes calcaires de Barthelemy. 



Marnes miocenes de Moissac. 



Binstead and Hordwell. 



