280 
TEE WASATCH EAUNA. 
preceding- pages. I will recapitulate them with reference to the principles 
laid down in my essay “On the Homologies of the Molar Teeth of the 
Mammalia Educabilia”.* 
The two striking features in the dental characters of the known mem¬ 
bers of this fauna are the absence of the two most specialized types of Mam¬ 
malian dentition, the sectorial and the Selenodont. The simple or slightly- 
modified Bunodont type characterizes the Bodentia, Mesodonta, Calamodon, 
and the uncertain PJienacodtts, —that is, eighteen species; the flesh-eating 
forms {Creodoiita), thirteen species, present the strong modification of the 
Bunodont dentition, which I have called the tubercular sectorial. Two 
external crescents are only developed in the ten species of Perissodactyla. 
In nine of these, the inner primitive tubercles remain, constituting the lowest 
(“Symborodont”) type in the order; while in one {Hyracliyus singularis), 
they are continued into transverse crests, forming the “Tapirodont”, or 
second grade of dental complication in the order. The third, or “Seleno¬ 
dont”, as already remarked, is wanting. Another Lophodont type is pre¬ 
sented by CorypJwdon (the “Bathmodont”), where only one outer crescent 
is developed, with one outer tubercle, and no inner ones remain. The his¬ 
tory of this peculiar dentition is unknown, but it is not more specialized 
than the Tapirodont type. 
It thus appears that of fifty-four species, thirty-five are Bunodont in 
their dentition and eighteen present a low and one a middle grade type of 
Ijophodonts. This fauna presents rather more primitive characters than 
that of the Bridger beds, where Tapirodonts are very abundant {Hyrachyus'). 
In the White Biver Miocene beds, the Selenodont and sectorial dentitions 
appear in strong force. 
In reviewing the evidence brought together in the preceding pages of 
this chapter, the writer is of the opinion that the type of brain shown to 
exist in the Amhlypoda and Creodonta is as distinct from those characterizing 
the primary divisions of the Mammalia as they are from each other; and 
that it necessitates the establishment of a special subclass for their reception, 
of equal rank with the groups Gyrencephala^ LissencepUala, and Lyencepliala. 
* Jouru. Acad. Pbila., 1874. 
