The Artiodactyla. 1087 
Xiphodontotherium. 
Protoreodon. 
Xiphodon. 
Rhagatherium. 
S 
lz 
The hypothetical! genus 1 is simply a bunodont without diaste- 
mata, and with well-developed canines. 
The genera of this family are Old World, except Protoreodon, 
which is North American. The Xiphodon gracilis Cuv. is one 
of the most abundant species of the Gypse of Paris and its equiva- 
lents. The restoration of Cuvier shows it to have been a graceful 
animal, with slender legs and neck. In Prootreodon S. and O. we 
first see the enlargement of the fourth inferior premolar (first olim) 
to function as a canine, which afterwards became such an important 
character of the Oreodontidæ. Probably two species are known, 
both from the Uinta formation of Utah; the? “type, P. pavous 
Scott and Osborn, IEN about the size of a raccoon. 
aT EREL EA VA e 
The Hippopotamidæ embraces a considerable variety of genera, 
which are spmetimes arranged in separate families. They are as 
follows :— 
I. Digits four. 
A, Metapodials distinct, distally keeled behind only; inferior 
incisors straight, patagiiidro ane os 
Six lower i incisors ; orbit cl rotodon Caut. Fale. 
Four lower incisors; orbit closed t Linn. 
Two loweri incisors ; orbit not closed . Cheeropsia Leidy. 
AA. Meepodials distinct; inferior incisors normal (Hyotheriine). 
Canines small, the inferior not received into a notch of the upper 
jaw ; premolars 4 ; fourth with two external tubercles; 
Hyotherium von. M. 
