1915.] Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas. 451 
form, moderate width, minute conules, no mesostyle, and smooth enamel 
characteristic of Omomys; the premolars agree with that genus in their 
moderate width, triangular form and strong deuterocones. If this upper 
jaw be correctly referred, the species is properly referable to the genus. In 
Tetonius and Absarokius the molars are wider, more oval in form, m? more 
reduced, conules better developed; the premolars larger proportionately, 
wider transversely in Tetonius, the deuterocones more reduced in Absarokius 
and much more in Uintanius. 
The alveoli of the front teeth in No. 16213 are partly shown. In front 
of p® are three small alveoli, the first two rather obscurely shown. These 
are probably an incisor, canine and p?, but the front of the jaw is not well 
enough preserved to distinguish the maxillo-premaxillary suture, so that 
the interpretation is doubtful. 
Hemiacodon Marsh 1872. 
Hemiacodon Marsu, 1872, Amer. Journ. Sci., Vol. IV, p. 212; Wortman, 1904, 
tbid., Vol. XVIT, p. 135, figs. 128-132. 
Tupe, H. gracilis Marsh from the Upper Bridger beds on Henry’s Fork, Wyoming. 
@: 
: ee) 23 ; 
Generic characters: Dentition 5133 F* with strong deuterocone, upper molars 
wide transversely with strong conules, distinct protostyle and hypocone, no mesostyle, 
m3 unreduced, lower molars with median paraconid, reduced on ms, vestigial on ms, 
no metastylid, trigonids relatively small, entoconid of ms; distinct; premolars not 
enlarged or crowded, p3_4 with triangular bases, deuteroconid distinct on ps. Canine 
and first incisor moderately large, second incisor and p2 very small. Jaw slender 
and rather shallow anteriorly, front teeth semi-procumbent. Enamel of molars and 
premolars heavily wrinkled. 
This genus is confined to the upper part of the Bridger formation, where 
it is represented by two or more species, larger than any other Eocene 
Tarsiide. It is nearly related to Omomys and may be regarded as a deriva- 
tive of that genus. Although fairly common, the skull is unknown and no 
skeleton material has been found associated with upper or lower jaws which 
were certainly of the same individual. Part of a skeleton associated with 
teeth of Telmatolestes and Hyopsodus is referred to Hemiacodon provisionally ; 
it certainly does not belong to either of the two genera whose teeth were 
found with it; and among the known genera of appropriate size Hemiacodon 
and Microsyops are the only ones which are not excluded, either by direct | 
or reasonably conclusive indirect evidence that their skeleton construction 
was widely different. If Microsyops is related to Mixodectes it is also 
excluded, but this is very doubtful. The reason for referring this partial 
skeleton and a number of isolated bones, of the same characteristic structure 
