ZOOLOGICAL POSITION AND STRUCTURE 35 
were likewise wanting in Gelocus does not appear to 
be ascertained. 
Gelocus and the other Tragulidce are believed to 
trace their ancestry to Pantolestes, a small general- 
ised ungulate from the Lower Eocene rocks of 
North America, of which only the cheek-teeth and 
some of the bones of the hind-foot were known when 
Professor Zitell's treatise was written. The upper 
molars have very low, somewhat triangular crowns, 
each carrying three blunt tubercles, arranged in a 
triangle, with two smaller subsidiary ones, this type 
of dentition being known as the bunodont, from the 
Greek bounos, a hillock, and odons, a tooth. Very 
probably the feet were severally furnished with four 
toes; and the navicular and cuboid bones of the 
tarsus are known to have been distinct, while the 
fibula of the leg articulated with the calcaneum of 
the tarsus in the manner characteristic of mammals 
with unspecialised feet, such as man and the dog. 
The Pantoiestidce, as the family to which the one 
known genus belongs has been named, represents 
the most primitive and generalised of all the Artio- 
dactyla, and the one which has given origin to 
all the rest. 
The Lower Eocene strata of North America have, 
however, yielded the remains of a still more primitive 
type of ungulates, namely, Phenacodus, of which the 
entire skeleton is fortunately known. This was a 
small animal with five-toed feet, in which the entire 
sole was applied to the ground in walking, in what 
is known as the plantigrade fashion, as exemplified 
by bears, as distinct from the digititrade style, in 
which, as seen in dogs, walking is done on the toes 
alone. The two rows of small bones of the wrist- 
