1881. } 395 
(Cope. 
It may be observed in conclusion that a successive increase of size in the 
species of this line has taken place in North America with the advance of 
geologic time. Thus, their probable ancestors of the genus Triplopus were 
the least of all. The Cenopoda of the White River formation were larger ; 
the oldest C. mite, being the smallest. The Aphelopes of the Loup River 
or Upper Miocene formation were all larger, and were nearly equal to the 
large existing species. 
TAPIRID &, 
The genera of this family are not numerous as yet. The oldest, Listrd- 
odon, appears in the Middle Miocene (Gers, France), and Tapirus is first 
found in the Upper Miocene (Epplesheim). The recent species of the fam- 
ily belong to Tapirus L., and Hlasmognathus (Gill). A small species, 
the Tapirulus hyrucinus Gerv., is from a bed at Perreal, France, which 
Pictet has identified with the gypsum of Paris (Oligocene). It is sgome- 
times referred to this family, but is not sufficiently well known to deter- 
mine its position. In America, Listriodon, or a genus which has not yet 
been distinguished from it, is found in the Miocenes. 
The three genera are distinguished as follows : 
Three anterior premolars different from fourth premolar 
and true molars ; last inferior molar with heel........ Listriodon. 
One superior premolar different from true molars; no heel 
of third inferior molar ; nasal septum cartilaginous.... Tapirus. 
Like Tapirus, but nasal septum osseous.........-+ w.s.... Blasmognathus. 
CHALICOTHERIID A, 
Gill; Cope, American Naturalist, 1881, p. 340. 
This family had numerous representatives during Eocene time, and a 
few species of Chalicothertwm extended into Miocene time. The bound- 
aries which separate the family from the Lophiodontide@ on the one hand 
and the Menodontide on the other, are not always easy to determine. 
From the former the symmetrically developed external Vs of the superior 
molars, and the double Vs of the inferior molars distinguish it. Yet in Rhaga- 
therium the external Vs are not so well distinguished as in other Chalico- 
thertide ; and in Propaleotherium, the anterior cingular cusp produces a 
part of the assymmetry found in the Lophiodontida. The character of the 
double inner cusps of the superior premolars, which distinguish the 
Menodontida, is only applicable to the last premolar in Diplacodon of the 
latter, while a trace of the additional cusp of this tooth is found in the 
Chalicotheroid Nestorithertwm. 
In using the following table it must be borne in mind that the number of 
the toes has been determined in a very few of the genera. Should any 
of them prove to have but three digits on the anterior foot, such genera 
must be referred to a new family intermediate between this one and the 
Paleothertida. ' 
PROC. AMER. PHILOS. 800. xIx. 108. 2x. PRINTED MAY 16, 1881. 
