378 The American Naturalist. April, 
true molars of Protogonodon are of the sextubercular type, I believe 
they should be associated with a superior molar which is tritubercular. 
These upper molars consist of three principal cones with well devel- 
oped intermediate tubercles; the external cones differ considerably in 
form from those of the Creodonta ( Sarcothraustes ), but the general 
form of the upper true molars in Protogonodon closely resembles that . 
of the Creodonts. _ 
Another character of the teeth of Protogonodon which differentiates 
it from the Perissodactyle line is the character of the inferior premo- 
lars. The last tooth of this series is much simpler in structure than in 
Protogonia, and closely resembles that of Pantolestes. It consists of a 
simple cone with a slightly enlarged heel. In Protogonia puercensis 
on the other hand, a well marked deuterocone is present, and this tooth 
is nearly as complex as it is in Phenacodus. 
_ I believe from these characters of the teeth, and also from the fact 
that the lower jaw is elongated and slender, as in the genus Pantolestes, 
that Protogonodon should be placed near the latter genus, and may 
stand in ancestral relation to it. 
Unfortunately the foot structure of Protogonodon is totally unknown, 
so until that is discovered we cannot decide its affinity with certainty. 
It is of great interest to note, if my supposition be correct, that in 
the genus Protogonodon we are dealing with an ancestral Artiodactyle, 
and that already as far down as the lowermost Eocene ( Puerco ) the 
main types of the Ungulata were differentiated. It will not then be 
necessary to resort as Schlosser has done to derive the Artiodactyla - 
from any of the known Periptychide, but that the Perissodactyla were 
represented by Protogonia,‘ the Artiodactyla by at least Prutogonodon 
and perhaps other genera, as suggested by Professor Scott. Lastly a8 
Professor Cope has shown the Amblypoda were already evolved and 
represented by the genus Pantolambda. 
Whether or not these Ungulate stems were in all cases distinct from 
the Condylarthra, remains for future research to prove; but at least 
one of them, the Amblypoda, was differentiated. In the case of Proto- 
gonodon the structure of its teeth shows that it was fairly well on the 
Artiodactyle line, but the discovery of its foot structure will demon- 
strate whether or not it had passed the Condylarthrous stage. 
I believe that among the Puerco Condylarthra that Protogonia was 
a persistent type, and nearly all of the Periptychids with the possible - 
‘Professor Cope informs me by letter that the name Protogonia is preoccupied, 
and he proposes as a substitute the name Euprotogonia. 
