1915.] 
Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas. 4] 
Vassacyon promicrodon (Wortman 1899). 
Uintacyon promicrodon Wortman (& Marrurw) 1899, Bull. A. M. N. H., Vol. 
XII, p. 111; (Prodaphznus) WortTMAN 
1901, Amer. Journ. Sci., Vol. XI, p. 30; 
(Vassacyon) Marrnew 1909, U.S.G.S. 
Bull., 361, p. 98; Mem. A. M. N. H., 
Vol. VI, p.37, pr. xia; fie, 4: 
Type, Am. Mus. No. 81, a lower jaw 
with ps-m; from the Wasatch of the 
Big Horn Basin, probably Systemodon 
zone. 
Distinctive characters: P:-m3; = 40; 
mi-3 = 19. Other characters given 
under the genus. 
To this species are referred Nos. 
15163, skull; 15161 parts of skull 
and jaws with a large part of the 
skeleton; 15160 skull, lower jaws 
and several limb bones; 15162, 
15164, ete., lower jaws. All are 
from the Systemodon zone of the 
Gray Bull in the Big Horn Basin. 
No. 84, a fragment of lower jaw 
with ms and the heel of mz was con- 
sidered by Wortman a possible suc- 
cessor of this species in the Wind 
River (Lost Cabin zone). It is 
otherwise unknown from any later 
horizon. 
This species is readily recogniza- 
_ ble by the peculiar thickening of the 
lower border of the jaw externally 
along the symphyseal region. This 
is associated with a flattened lower 
canine, and a somewhat triangular 
but curved upper canine. 
SS 
S> 
7 
es [ 
G { ' 
| 
\ ) AW 
Fig. 35. Vassacyon promicrodon, skull, top 
view, natural size. No. 15163, Gray Bull 
beds, Big Horn Basin. 
