1090 The Artiodactyla. 
Day beds of Oregon another species of this genus is found, the Æ. 
imperator of Leidy, which was little inferior in dimensions to the 
E. ramosum. The greater part of its skeleton is known. 
The pigs (Surpm) are modified and specialized descendants of 
some form allied to Paleocherus. Chronologically speaking they 
are of rather modern origin. The genera are as follows: — 
(a) Molars and superior incisors not reduced; the former not 
covered with cement; superior canines recurved (Suinz). 
Molars with cusps united into transverse crests, Listriodon Meyer. 
Molars with four much plicate tubercles on each . 
A R < teenei a i aa isai a app ohyts Cantl aie 
Molars with numerous irregular accessory lobes; premolars $ 
jasi ivs Sus Linn. 
s..... 
No accessory lobes; premolars 2 Babirussa Cuv. 
(aa) Superior incisors reduced in number; molars reduced in 
number, and the valleys filled with cement (Phacocheerinz). 
Superior incisors one; premolars none; molars 3, with numerous 
tubercles; superior canines recurved.............+. Phacocherus Cuv. 
FIG. 5.—Coloreodon ferox Cope, skull from the John Day Miocene of Oregon, one- 
half natural size. 
Listriodon and Hippohyus are the only genera of Suide which 
are extinct; but the extinct species of Sus are more numerous. In 
_ Listriodon the molar teeth are so tapir-like as to have led to its 
being placed in the Perissodactyla. When the skeleton was ob- 
