18 INTRODUCTION. 
4. Those which possess true horns, and have neither upper canines nor incisors; 
as Antilope, Bos, Ovis, ete. 
The Puridigitata ordinaria are represented by Sus, Dicotyles, Hippopotamus, Choe- 
ropotamus, Anthracotherium, Hyracotherium, etc. 
The second sub-order of Ungulata is divisible into the following families :— 
Solipedia, represented by Equus, Hipparion, Anchitherium, ete. 
Ordinaria, to which belong Rhinoceros, Tapirus, Pulwotherium, ete. 
Proboscidia, containing Elephas and Mastodon. 
Of the mammalia from Nebraska, which will be described according to the pre- 
ceding arrangement, there are seven species of four genera which belong to the 
Ruminantia, two species of one genus to the Puridigitata ordinaria, one species to 
the Solipedia, and four species of three genera to the Imparidigitata ordinaria. 
The exceptional case above referred to, belonging to a different order from the 
Ungulata, is a carnivorous animal of the feline genus Machairodus. 
The chelonian fossils from Nebraska, of which there are five species, belong all 
to the genus Testudo. 
