1060 The Perissodactyla. [Dec. 
Ocean; for, if the transportation of the pebbles and sand was 
really due to the tide, it would indicate the existence of an At- 
lantic basin in pre-palezozoic days, from which the forced wave 
flowed over or through these successive reefs or ledges into the 
midland basin. 
THE PERISSODACTYLA. 
BY E.D.COPE. ` i i 
(Concluded from page 1007.) 
T CHALICOTHERIIDÆ had numerous representatives during 
Eocene time, and a few speċies of Chalicotherium extended 
into Miocene time. The boundaries which separate the family 
from the Lophiodontidæ on the one hand and the Menodontide 
on the other are not always easy to determine. From the former 
the symmetrically-developed external V’s of the superior molars 
and the double Y’s of the inferior molars distinguish it; yet in 
Pachynolophus the anterior cingular cusp produces a part of the 
EPA -g 
kat at pi 
. l : 
pi Pe b 
from Wind ; 
River Eocene of Wyoming. From Wortman, after Cope. , Fig. a, sec nd superior 
molar; 4, last inferior molar. ae and fe, anterior and posterior €x 
a 
Fic. 24. Lambdotherium popoagicum Cope, molar teeth, natural size; 
and 
rior internal tubercles; acc and fcc, anterior and posterior intermediate tubercles; k 
h, heel. 
asymmetry found in the Lophiodontide. The character E s : 
double inner cusps of the superior premolars, which disti eee 
the Menodontidz, is only found in the last premolar in Dip eer . 
of the latter, while a trace of the additional cusp of this oe 
found in the Chalicotheroid Nestoritherium. a that the 
In using the following table it must be borne in mind of the 
structure of the feet has not been determined in Sev 
genera: : 
