1915.] Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas. 339 
the three molars (No. 4679), from the Wasatch of the Bighorn basin. 
Cope differentiated it from P. primavus by the presence of accessory cusps 
on the anterior and posterior slopes of metaconid. In his Tertiary Verte- 
brata Cope recognized that these characters were merely individual vari- 
ations. 
There is, among the specimens which I have referred to P. primevus, 
a considerable variation in size, relative width, and general robustness of 
the teeth. And since the specimens showing these variations fall into 
ee :* P. voritmant 
\ (Topotype, Lost Cabin beds, 
? Wind River basin, Wyo.) 
P. brachypternus 
(Topotype, Gray Bull beds, Big- 
horn basin, Wyo.) 
Fig. 8. Lower teeth, external view, of species of Phenacodus. 
rather well defined groups, it seems well to consider these groups as 
of subspecific rank, one group being smaller than the plesiotype, the 
other larger. 
Phenacodus primevus hemiconus Cope, 1882. 
Phenacodus hemiconus, Proc. Am. Phil. Soc., 1882 , De 1707 1885, Tent. y ert...p. 
463, pl. xxve, fig. 16. 
Type, Amer. Mus. Cope Coll. No. 4391, a fragment of the upper Jaw 
with the second and third unworn molars; ?Gray Bull Beds; Bighorn basin, 
Wyo., J. L. Wortman, 1881.. 
The chief distinctions from P. primavus pointed out by Cope were the 
smaller size and the rudimental character of the hypocone and metacone 
in m’. The size of the cusps on this tooth is variable within specific limits 
and while the individual is somewhat smaller than the type of P. primevus 
yet it seems that it is hardly sufficient to keep it separate as a distinct 
species. Eleven specimens from the Gray Bull beds and one from the Lost 
Cabin are referable to this small variety. Of these I select for illustration 
a topotype consisting of a palate and lower jaws (No. 15286), from the 
Gray Bull beds, with the third premolar to third molar, above and below, 
well preserved igs, 3,5, 7). The agreement in size and structural char- 
acters with Cope’s type are very close. 
