1915.] Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas. 45 
thew, 1909) is confirmed by a more careful study of their characters, with 
the additional material now at hand. Although the second lower molar 
is smaller than the first, it is the tooth which in conjunction with the first 
upper molar is progressively specialized as a shearing tooth. The fourth 
upper premolar and first lower molar, although large teeth, have very little 
shearing action, as is clearly shown by the wear of these teeth, and the suc-. 
cessive species show a decided tendency to reduce these teeth wholly to the 
crushing (or bone-breaking?) function of the premolars. The same is true of 
Patriofelts and to a less marked extent of Oxywna and the Limnocyon group. 
In all the Oxyeenide the carnassial angle is behind m!; that is to say, the 
outer line of the dentition is angulate at that point, the teeth in advance of it 
being extended posteroexternally, those behind it anteroexternally, a more or 
less pronounced pit (Hntodiastema of von Ihering) for the reception of the 
lower carnassial being developed in the palate. In the Miacide the carnassial 
angle is behind p‘, in the Hyzenodonts behind m?. This is a much more relia- 
ble guide to the affinities of the genera than is the relative size of the teeth, and 
conforms to a variety of differential family characters of skull and skeleton. 
The Oxyeenid genera do not stand in any exact successional relationship. 
Patriofelts cannot be derived from Oxyena, nor from Palewonictis or Ambloc- 
tonus but from some intermediate type agreeing with the last named genus 
in the premolars and zygomatic arches and with the first named in the 
molar teeth. Paleonictis and Ambloctonus are very closely allied but ap- 
pear to be divergent or at all events distinct lines of specialization. Oxyena 
is represented by a series of species in which the shear is progressively 
perfected and concentrated on mz, premolars and molars showing a marked 
analogy to those of the Felidae. The short head, deep arches, very short 
deep jaw, massive premolars, robust and much worn shearing teeth of 
Patriofelis and Paleonictis and Ambloctonus are analogous to the Hyznide, 
but not so closely. The smaller Oxyzenids, Limnocyon and its allies, offer 
a broad analogy to the Viverride; and just as the Felide and Hyznide are 
structurally derivable from the Viverride, so are the larger and more 
specialized Oxyeenide structural derivatives of the Limnocyon group. Of 
the two genera which represent this last group in the Lower Eocene, one, 
Prolimnocyon, has the most primitive dentition of any Oxyeenid; the other 
Dipsalidictis, with the dentition of Limnocyon, has the primitive foot- 
structure of Oxyena. But Oxyena itself occurs in the Clark Fork horizon 
along with Dipsalidictis, so that the common ancestry of the genera was well 
down in the Paleocene.! Each genus includes one or more phyla of true 
genetic descent, so far as one may judge from the evidence. 
1 But the ancestral types have not been found, or at all events have not been recognized 
in the Puerco and Torrejon faunz, and hence the family Oxyeenidee must be regarded as an 
immigrant group appearing in North America at the close of the Paleocene. 
