Cope.] 380 [April 15, 
| EOCENE. MIOCENE. 
| RECENT. 
i} r i: 
Lower| Upper Lower Middle Upper, 
Menodontide. 
Acoéssus Cope........... cece eee cee 1 
Diplacodon Marsh.................055 1 
Menodus Pom...............ee0 senses 2 
Symborodon Cope...........-...0.005 6 
Deeodon Cope ......... 005 cece eee eeee 1 
Paleothertida. 
Anchilophus Gerv...............0000 
Paloplotherium Ow............ 2.200. 
Paleotherium Cuv............-..000eee 
Mesohippus Marsh..................05- 2 
Anchitherium Kaup.............20.00+ 2 
Anchippus Leidy............00.0.eeee 
Hippotherium Kaup.............-..4. 
Protohippus Leidy .................005 i 
CO 
atta 
(>) ie old 
ee 
Equide. 
Hippidium Owen.................0005 : 2| 3 
HQUUS Linn,» ccocees cee cwesemensesss 5! 7 
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 Lophiodontide and Chalicothertide ; those of the 
Miocene are Rhinocerontide and Paleotheriide. The Tapiride and Equide 
characterize the latest tertiary epochs. A genealogical tree of the order 
may be constructed as follows : 
Equide. 
Rhinoceride. Paleeotheriide. 
: ae eos 
Hyracodontide. Tapiride. 
= ; 
Triplopide. Menodontide. 
ee \ rd 
Lophiodontide. Chalicotheriide. 
Sy a 
Hyracotheriine. 
The types of the Lophiodontide and Chalicothertide differ only in the two 
