42 Bulletin American Museum of Natural History. [Vol. XXXIV, 
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‘Fig. 36. Vassacyon promicrodon, external view of lower jaw and crown views of upper 
and lower teeth, natural size; from skeleton No. 15161, lower Gray Bull beds of Big Horn 
Basin. 
OXY ANID. 
Family characters:' Carnassials m3, third molar absent.2_ Skull robust, basicranial 
region wide, jaws stout with strong symphysis. Lumbar zygapophyses cylindrical 
or revolute. No supratrochlear foramen on humerus. Manus and pes mesaxonic, 
claws fissured at the tip. 
The Lower Eocene representatives of this family belong to three groups, 
(1) Oxyena, large, predaceous types with powerful shearing molars; (2) 
Paleonictis and Ambloctonus, large, short faced types with robust teeth 
adapted for breaking (? bone-breaking) and shearing; (3) Dipsalidictis and 
Prolamnocyon, smaller and more primitive genera with tuberculosectorial 
molars. These three groups correspond in adaptation to the Felide, Hye- 
nidz and Viverridee among modern carnivora. 
Oxyena is well known from the descriptions of Cope and Wortman, and 
while fairly abundant in the Lower Eocene the new material adds little to 
the morphology. Paleonictis and Ambloctonus are much searcer, and of 
their skeletal construction very little is known. The new genus Dipsali-. 
dictis from the Clark Fork has the very primitive dentition of Limnocyon 
but lacks the progressive characters of the feet of that Middle and Upper 
Kocene genus, the feet being the most primitive known among Oxyeenide. 
a ee Norte i ae On le nels pag ee 
1 Matthew, 1909, Am. Mus. Mem., IX, 327. 
2 Except in Prolimnocyon infra. 
