1877. ] The Suessonian Fauna of North America. 99 
of fifty-four had been discovered. The teeth of the remaining 
forty-two species are bunodont or tubercular only, and in most 
cases simple forms of that type. 
Another marked feature of the Suessonian or Wahsatch Mam- 
malia is the possession by the greater number of them of five 
toes on both of the feet. The only probable exceptions to this 
rule are the ten species of Perissodactyla already mentioned, and 
perhaps a very few others. The genera of later and the present 
periods with three toes on all the feet, with two functional toes, 
and one toe, are wanting in this fauna. 
It was also asserted that nearly. all of the species were planti- 
grade in their mode of progression, that is, that the soles of the 
fore and hinder feet were applied to the ground, instead of being 
obliquely elevated behind, the heel thus appearing to form an an- 
gle of the leg, as in most living mammals. It is well known that 
among recent quadrupeds the Quadrumana, Plantigrade Carniv- 
ora, Proboscidia, and some Rodentia and Edentata, are planti- 
grade, while the others are digitigrade. The only species of the 
Wahsatch fauna possibly digitigrade are the species of Perisso- 
dactyla, already mentioned, although it was stated that the struc- 
ture in a few of the other genera is yet unknown. 
The agreement of clawed and hoofed (unguiculate and ungu- 
late) mammals of this period in the general imperfection of the 
structure of the brain, of the ankle and elbow-joints, and in the 
position and number of the toes, was dwelt on as an important 
fact. It did not however warrant the separation of all the Mam- 
malia of the Suessonian as a distinct order, on account of the ex- 
ceptions pointed out. The clawed types presenting these char- 
acters have been since! defined as an order, under the name of 
Bunotheria, which it was believed might embrace also the exist- 
ing Insectivora as a suborder. The ungulates of like character 
have already been erected into a distinct order, the Amblypoda, 
which includes two suborders, the Pantodonta and Dinocerata. 
The only mammalian orders of that period still existing are then 
the Perissodactyla and Rodentia. 
Proceedings Academy, Philadelphia, 1876, page 88 
