LOWER MIOCENE, UNITED STATES. 
. 249 
limestone, marls, and siliceous clay, described by Dr. D. 
Dale Owen,* in which many bones of extinct quadrupeds, 
and of chelonians of land or fresh-water forms, are met with. 
Among these, Dr. Leidy describes a gigantic quadruped, 
called by him Titanotherium^ nearly allied to the Palmothe- 
rium^ but larger than any of the species found in the Paris 
gypsum. With these are several species of the genus Ore- 
odon^ Leidy, uniting the characters of pachyderms and rumi¬ 
nants also; Mucrotaphiis^ another new genus of the same 
mixed character; two species of rhinoceros of the sub-genus 
Acerotherium^ a Lower Miocene form of Europe before men¬ 
tioned ; two species of Archmotherium^ a pachyderm allied 
to Chmropotamus and Hyracotherium; also Pmhrotherium^ 
an extinct ruminant allied to Poreatherium^ Kaup; also 
Agriochoerus^ of Leidy, a ruminant allied* to Merycopotamus 
of Falconer and Cautley; and, lastly, a large carnivorous 
animal of the genus Machairodus^ the most ancient example 
of which in Europe occurs in the Lower Miocene strata of 
Auvergne, but of which some species are found in Pliocene 
deposits. The turtles are referred to the genus Testudo^ but 
have some affinity to PJmys, On the whole, the Nebraska 
formation is probably newer than the Paris gypsum, and 
referable to the Lower Miocene period, as above defined. 
* David Dale Owen, Geol. Survey of Wisconsin, etc, ; Philad., 1852. 
11 * 
