Cope.] 



380 



[April 15, 



Menodontidce. 



Acoessus Cope 



Diplacodon Marsh. 



Menodus Pom 



Symborodon Cope. 

 Dseodon Cope 



Palceotheriidw. 



Anchilophus Gerv. . . 

 Paloplotherium Ow. . 

 Palaeotherium Cuv. . . 

 Mesohippus Marsh. . . 

 Anchitherium Kaup.. 



Anchippus Leidy 



Hippotherium Kaup. 

 Protohippus Leidy . . 



Equidm. 



Hippidium Owen . 

 Equus Linii 



Total number of well determined species, one hundred and eighty-nine. 



From the preceding table it can be readily seen that this order was 

 abundantly represented during the Eocene period, and that the recent 

 species are comparatively few. It may also be observed that certain fami- 

 lies predominated during certain periods. Thus the prevalent Perissodac- 

 tyla of the Eocene are LopModontidce and ClialicotheriidcB ; those of the 

 Miocene are Bhinocerontidae and Pal(Bothemdce. The Tapiridm and Equidm 

 characterize the latest tertiary epochs. A genealogical tree of the order 

 may be constructed as follows : 



Equidse. 



Rhinoceridse. 

 Hyracodontidse. / Tapiridse 



Triplopidse. 



Lophiodontidse 



Palaeotheriidge. 



Menodontidae. 



Chalicotheriidge. 



Hyracotheriinse. 

 The types of the LopModontidm and GhalicotJienidce differ only in the two 



