1915.| Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas, 331 | 
Cabin. In the Clark Fork beds the family predominated to a still greater 
extent than in the Torrejon, at least three-fourths of the specimens obtained 
from this horizon being of this family and the collecting was done at various 
levels and over a considerable areal range. —Phenacodus is fairly common in 
the Clark Fork, most abundant in the Gray Bull and fairly common again 
in the Lysite and Lost Cabin. Kctocion is most abundant in the Clark Fork, 
e 
EctTocion 
Lower Eocene 
PHENACODUS 
Lower Eocene 
TETRACLAZNODON 
Basal Eocene 
Fig. 2. Outlines of lower cheek-teeth of the three genera of Phenacodontidaz. 
common in the Gray Bull, absent from the Lysite and rare in the Lost 
Cabin. In the New Mexico horizons Hctocion is absent while Phenacodus 
is rather uncommon in the lower and rare in the upper level. 
Key to Genera of Phenacodontide. 
A. Mesostyle rudimentary or absent..............++64- Pe oe Tetraclenodon. 
B. Mesostyle well developed ~ 
b. Teeth bunodont, mesostyle and metacone weak on m', ps with entoconid 
weak or absent, p3; with low posterior basal cusp. M! and m? with meta- 
conule on a line between metacone and hypocone or posterior to it. 
Phenacodus. 
bb. Teeth more or less lophodont, mesostyle and metacone well developed on 
m3; p, with strong entoconid, ps with high compressed posterior basal cusp; 
m! and m? with metaconule anterior to a line between metacone and 
hynoeOGiesc or ids ce a FA nih Ra ee aE eM es ok wa ae Ectocion. 
