NO. I LOWER EOCENE MAMMALIAN FAUNAS — GAZIN 63 



I note that although the paraconid is persistent on Mi and occasionally 

 on M2, the entostylid is rather variable. The presence of an ento- 

 stylid would not seem to be necessarily an advanced character, because, 

 although it is rather common in the Bighorn Gray Bull materials, it 

 is usually weak or absent in the La Barge Knight specimens. 



An isolated upper molar from the Red Desert locality east of 

 Steamboat Mountain may also be referred to Hyopsodns loomisi, but 

 the species does not seem to be represented in the Fossil Basin 

 collections from west of Elk Mountain. 



HYOPSODUS, cf. MITICULUS (Cope) 



Jaws, maxillae, and isolated teeth that may be referred tentatively 

 to Hyopsodns miticulns are included in the collections from the hori- 

 zons of lower Gray Bull equivalence in the Knight. Reference of 

 these, however, to the geographically remote New Mexican species 

 may be questionable. Most of the material represents relatively small 

 individuals, corresponding to about the lowest part of the size range 

 determined for Gray Bull materials referred to this species. However, 

 the largest individual represented in the Bitter Creek sample (Y.P.M. 

 No. 14052) is just under the mean for the Gray Bull. Some that seem 

 not referable to H. loomisi are smaller than any in the U.S.N.M. 

 Gray Bull sample, but it should be noted that the latter does not 

 include Sand Coulee Hyopsodus material. 



To Hyopsodus miticulus are also referred specimens from the 

 Lysite equivalent in the Fossil Basin, materials that might otherwise 

 have been identified as Hyopsodus lysitensis or Hyopsodus mentalis 

 lysitensis. In a statistical study of Hyopsodus, currently under way, 

 I find that the range of measurements for specimens of the smaller 

 form, generally designated H. m. lysitensis, in the American Museum 

 and Princeton University collections from the Cottonwood Draw 

 Lysite, corresponds very well and is included within that for the H. 

 miticulus materials from the Gray Bull. I am unable to justify a 

 distinction on size or progressiveness. The frequency distribution for 

 size of teeth in Hyopsodus mentalis in a small sample from the Largo 

 beds of New Mexico is discordant with that for the Lysite materials, 

 although Van Houten (1945, p. 434) and Simpson (1948, p. 383) 

 have thought that that Largo may be more nearly Lysite than Lost 

 Cabin in age. I do not think that the Lysite Hyopsodus, if contempo- 

 raneous, is the same species as that recorded for the Largo. 



