282 
THE WASATCH FAUNA. 
terms of each corresponding with each other, as do now the genera of the 
Clamatores and Oscines, of the Ardfera and Ramformia, etc.” The exami¬ 
nation into the structure of the brains of the Eocene Mammalia^ prosecuted 
since the above was written, has resulted in the discovery of the subclass 
Protencepliala, which embraces a series of suborders which correspond in 
part to those now existing, which possess more fully-developed brains. The 
subclasses Protencephala and Gyrencepliala are homologous groups in the 
true sense of the term. And I have shown that the imperfection of the 
tibio-tarsal articulation closely accompanies the undeveloped type of brain, 
the only order possessing the grooved astragalus being also the only one 
which presents the other general characters of an existing order, the Peris- 
sodactyla. The following table represents the ancestral relations of the 
Amblypoda and Bunotlieria to the existing orders. As the Perissodactyla are 
the cotemporaries of these orders, I look for the discovery of the latter in 
still older beds, where they will appear as the ancestors of the former; and 
in this expectation I am encouraged by the reduction in numbers and va¬ 
riety of Perissodactyla in the older Wasatch, as compared with the newer 
Bridger beds. Moreover, the Wasatch Amblypoda, as ancestors of the exist¬ 
ing Ungidata, present a type of dentition too complex to represent the direct 
ancestors of the Bunodont types, such as Artiodactyla-omnivora and Probos- 
cidea; hence I look for the future discovery of Amblypoda with Bunodont 
dentition. The table is as follows, being in general features similar to one 
which I published in the Annual Report of the United States Geological 
Survey of the Territories for 1872, p. 648. It differs in the substitution of 
ordinal and subordinal names for those of genera, in accordance with the 
language used in the text accompanying it, 1. c., p. 647. 
Insectivora. 
Tceniodonta. Tillodonta. 
OTRENOEPHALA. 
Carnivora. Quadrumana. Proboscidca. 
LISSENOEPUALA. 
PROTENOEPUALA.' 
Oreodonta. Mesodonta, f. 
Perissodactyla. Artiodactyla. 
BUNOTnERIA. 
AMBLYPODA. 
