192 The American Naturalist. [ApriU 
To these general characters are added numerous subordinate 
peculiarities in the known genera and species, which make 
them among the most remarkable of living beings. These 
peculiarities are the result of a long period of development. 
It is one of the most curious facts of paleontology that the 
order does not make its appearance until the middle of the 
Miocene system, and the greater number of forms do not appear 
until the upper Miocene. That it existed earlier cannot be 
doubted, and that it originated from some Eocene condylar- 
thran is evident ; but the intermediate forms are entirely lost 
to us as yet, and the phylogeny of the order is absolutely 
unknown. This is the more extraordinary since the earliest 
known genus (Dinotherium) embraces only species of colossal 
size, and its immediate ancestors could not have been insig- 
nificant. We may regard Phenacodus as the first form we 
know of earlier than Dinotherium, but what a hiatus is ex- 
pressed in this statement ! It is to be anticipated that the 
gap will be filled by discoveries in Asia, or the Southern 
Hemisphere. South America may be probably excluded from 
this prospect, since the extensive researches made there by 
Burmeister, Ameghino, and Moreno, have not resulted in the 
discovery of any Proboscidia earlier than the Pliocene. Asi- 
atic investigations have revealed nothing, as the proper 
formations have not been found, and the same is true of 
Africa. So we shall have to wait until the paleontology of 
the present home of the order is exposed to view, before we 
shall know of the steps which lead from Phenacodus to these 
mighty monarchs of the animal kingdom. The absence of 
primitive Proboscidia from North and South America and 
Europe, impels us to believe that the representatives of the 
order known to us from those regions, are the descendants of 
immigrants from Asia and Africa. 
But two families of Proboscidia are known. They are de- 
fined as follows : 
Adult dentition embracing premolars and molars ; no su- 
perior incisors Dinotheriidce. 
Adult dentition embracing one or two true molars only ; 
superior incisors ElephantidcB. 
The family of the Dinotheriidae embraces one genus and 
