NO. 6 PALEOCENE FAUNAS OF BISON BASIN — GAZIN 23 



shorter diastema behind the incisor than in typical P. fodinatus. The 

 length of the diastema, though, is uncertain as the bone is incomplete. 



MEASUREMENTS IN MILLIMETERS OF TEETH IN SPECIMENS OF Plcsiadopis, CF. 



fodinatus jepsen 



U. of Wyo. 

 No. 1 08 s 



M*, anteroposterior diameter : greatest transverse diameter 3.8:5.9 



M*, greatest transverse diameter 5.5 



U. of Wyo. U.S.N.M. U.S.N.M. 



No. 1082 No. 20783 No. 20784 



P4, anteroposterior diameter : greatest 



transverse diameter 2.6 : 2.2 



Ml, anteroposterior diameter : greatest 



transverse diameter 3.6 : 2.9 3.2 : 2.9 



M2, anteroposterior diameter : greatest 



transverse diameter 3.6 : 3.4 3-9 : 3-6 



Ms, anteroposterior diameter : greatest 



transverse diameter 5-5 : 3-5 



PLESIADAPIS JEPSENI/ new species 

 Plate 4 



Type. — Left ramus of mandible with P4-M3, U.S.N.M. No. 20760. 



Horizon and locality. — Bison basin Tiffanian, ledge locality at south 

 rim of Bison basin, W^ sec. 28, T. 27 N., R. 95 W., Fremont County, 

 Wyo. 



Specific characters. — Close in size to Flesiadapis gidleyi and Plesi- 

 adapis anceps. P2 almost always present and hypoconulid portion of 

 talonid of M3 broad as in P. gidleyi. Lower teeth relatively broad 

 with outer walls decidedly sloping as in P. anceps and P. rex. Conule 

 weak to scarcely discernible on lingual slope of primary cusp of P^ 

 but prominent on P*. Mesostyle absent or very weak on upper molars, 

 M^ slightly more expanded posterointernally than in P. anceps. 



Discussion. — Plesiadapis jepseni is one of the better represented 

 forms in the Bison basin collection, exceeded in number of specimens 

 only by Phenacodus ? bisonensis and Gidleyina wyomingensis. About 

 23 specimens, mostly lower jaws, are for the most part divided be- 

 tween the saddle and ledge localities below the south rim of the basin. 

 Two, however, came from the locality at the west end of the basin and 

 two from near the Titanoides primaevus locality in the southwestern 

 part of the basin. Three mandibular portions and one maxilla are 

 in the collections of the University of Wyoming. 



7 Named for Dr. Glenn L. Jepsen in appreciation of his work on the 

 Plesiadapidae. 



