1915.] | Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas. 315 
Principal diagnostic characters: skull mesaticephalic, occiput broad, mastoid 
exposure considerable, lachrymal exposed upon face, lachrymal foramen within 
orbital rim, zygomatic arches deep, nasals not expanded posteriorly, palate not 
fenestrated nor extended backward nor crested. on posterior margin; incisors unre- 
duced, pointed,” subspatulate, canines small, incisiform, premolars progressively 
complex, the anterior premolars, canines and incisors in both upper and lower jaw 
similar in size and character without diastemata, posterior premolars progressively 
complex in cusp constitution, submolariform; molar cusps tending to be round 
conical, upper molars six-cusped, conules prominent, hypocone progressively devel- 
oped, no external styles, lower molars with four principal cusps partly alternating . 
(the inner pair not opposite the outer pair), heels not basined, hypoconulids small. 
median, heel of ms comparatively short; humerus moderately expanded distally with 
entepicondylar foramen and supratrochlear vacuity, shaft of ulna wide but thin, 
olecranon large, radius with flattened oval head; carpals separate, lunar-unciform 
contact considerable; in pelvis iliac bar trihedral, ischium takes little or no part in 
symphysis, femur rather short, third trochanter prominent and situated well down 
on shaft, tibia separate from fibula; in pes, astragalus with short distinct neck, flat- 
tened head, tibial facet oblique, little grooved, no inner malleolar crest, foramen 
distinct, calcaneum with slight fibular facet, cuboid with distinct astragalar facet 
facing chiefly internal, five metatarsals, the lateral digits unreduced, distal ends hinge- 
jointed, phalanges short, unguals claw-like, fissured, not compressed. 
This genus is abundant in all the Eocene horizons above the Clark Fork. 
In the Clark Fork it is not found. 
Although skulls and skeleton parts are rare the species are represented 
in our Wasatch and Wind River collections by great numbers of jaws and 
parts of jaws, about one thousand altogether. The chief specific distine- 
tions are: size, length of teeth, differentiation of entoconid from hypo- 
conulid on m3; development of hypocone cn upper molars, size of m3 
and of heel of m3, form of pea and disappearance of the basined talonid. 
In these characters the oldest species approach near to Haplomylus, while 
the latest species approximate those of the Middle Eocene. 
The true horizons of the several Lower Eocene species have not hereto- 
fore been understood correctly, but the abundant comparative material 
makes them clear. The described species are as follows: 
. miticulus (Cope, 1874) Wasatch New Mexico. 
. mentalis (Cope, 1875) - Ay a 
lemoinianus Cope, 1882 Bighorn basin Wyoming. 
. powellianus Cope, 1885 , ‘i : 
. wortmani Osborn, 1902 Wind River basin 
. simplex Loomis, 1905 Bighorn basin 
minor Loomis, 1905 Wind River basin ee 
. brownti. Loomis, 1905 . if se 
. jacksoni Loomis, 1905 
6 
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All these are nearly allied to each other and to the Bridger species. 
H. lemoinianus appears to be a synonym of H. mentalis, and H. jacksone 
