1915.| Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas. 313 
Haplomylus gen. nov. 
Fam. ?Hyopsodontide. 
L'ype, Microsyops speirianus Corr, probably from the Lower Wasatch 
of the Bighorn basin, Wyo. 
This imperfectly known species was described by Cope from a lower 
jaw fragment with mj and provisionally referred to Hyopsodus and sub- 
sequently to Muicrosyops. Numerous additional specimens have been 
secured from the Bighorn basin, and show that it represents a distinct 
genus. | 
The lower molars consist of four cusps, somewhat obliquely set, but less 
so than in Hyopsodus, lower, and with a distinctly 
basined heel. The last molar is considerably re- 
duced. The fourth premolar is more compressed 
and elongate than in Hyopsodus, with the princi- 
pal cusp distinctly twinned, and a sharp narrow 
heel, and small anterior basal cusp. 
The upper teeth are of ovate-trigonal outline, 
with hypocone well developed but from the pos- 
terior wing of the protocone, so that it does not 
project postero-internally. The external cusps 
are rather small, with distinct para-, meso- and 
metastyles; the conules are small but distinct. y \ 
The fourth premolar is triangular with the prin- ay 
cipal cusp central, and three minor cusps at the Fig.1. Haplomylus speiri- 
int | t ternal and antero-external %”¥% Cope: No. 16107, Up- 
EY ae ee per, jaw and lower premolar, 
angles. The last upper molar is greatly reduced enlarged three diameters. 
Lae ike Sand Coulée beds, Clark 
and simpiied. Fork basin, Wyoming. 
The affinities of the genus appear to be with 
Hyopsodus and Mioclenus. 'Tarsiid relationship is improbable, judging by 
the compressed premolar and the general set of the molar cusps. . 
Haplomylus speirianus (Cope 1880). 
Hyopsodus speirianus Copp, 1880, Amer. Nat., Vol. XIV, p. 908; (Microsyops) 
1885, Tertiary Vertebrata, p. 216, pl. xxva, fig. 8; (‘‘Microsyops’’) OsBorn, 1902, 
Bull. Am. Mus. Nat. Hist., Vol. XVI, p. 210, fig. 37. 
Type, Am. Mus. No. 4190, a lower jaw fragment with three molars 
preserved. 
