1915.] Maithew and Granger, Lower Eocene Wasatch and Wind River Faunas. 345 
Distinctive Characters. P3-m3; = 33 mm. , Mi-3 = 20 mm.; py, elongate 
and narrow with very prominent paraconid, longer and narrower than any 
of the molars; ps with broad low heel and a small accessory cusp high up 
on anterior ridge of protoconid; ramus rather slender; weak metaconules 
on m?. | | 
Cope founded this species on “three mandibular rami — all displaying 
the fourth premolar” without specifying a type, but the measurements, most 
of his characters and the figures were drawn from No. 4396, which is much 
the most complete and which it seems proper to consider as the type, espe- 
cially since neither of the other fragments furnishes any characters not found 
in this one. This is the smallest species of the genus and in some respects 
the most primitive. The long compressed ps and the simple compressed 
pz serve to distinguish it from P. vortmani, the next largest species. Most 
of the specimens show on the fourth premolar a high trenchant hypoconid 
development and a steep slope down to. the inner side of the tooth without 
much trace of entoconid development. In most of the specimens there is a 
small accessory cusp in front of and between the protoconid and metaconid 
on the py. The last upper molar is much reduced in the four specimens in 
which this tooth is present, while the last lower molar varies from a slight 
to a marked reduction. In one specimen of badly worn upper and lower 
teeth (No. 15331) the p? is elongate with the inner cusp placed at the ex- 
treme postero-internal angle, opposite the posterior outer cusp. It isin the 
character of this tooth and of the lower premolars that this species is the 
most primitive of the genus. 
Occurrence. ‘Twenty specimens from the Gray Bull beds of the Bighorn 
basin, and two from the lower horizon of New Mexico are identifiable with. 
this species. Its»occurrence in the other horizons has not been noted. 
From the upper beds of New Mexico, near Ojo San Jose, is a finely pre- 
served maxilla (Fig. 10) with 
the canine and all cheek teeth 
(No. 16249). It is slightly 
larger than the type of P. 
brachypternus and differs in 
having the m? but slightly 
reduced and with well devel- Fig. 10. Phenacodus (?)brachypternus, upper teeth, 
crown view. Largo beds, San Juan basin, New 
oped metacone and meso-  qgoxieo. 
style; p* is unusually broad 
antero-posteriorly and shows a metaconule. The third premolar is elongate 
and primitive in construction; p? is slightly expanded posteriorly and with 
a small cusp at the postero-external angle; p' is double-rooted, a condition 
not observed in the ten other specimens of Phenacodus in which this part 
