6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



1941 specimen, verifying the tentative assignment of the Buckman 

 Hollow Almy form made in 1942. U.S.N.M. No. 20785 has lower 

 molars a little broader than in the type, perhaps more noticeable in 

 M3, but no doubt this is within the range of individual variation. 



The last upper molar (U.S.N.M. No. 21281) is considerably larger 

 than that (No. 16697) tentatively assigned to P. rubeyi but relatively 

 does not show so marked a posterior extension of the posterolingual 

 portion. It is also less expanded in this respect than in the type ma- 

 terial of P. cookei. Its measurements are 6.8 mm. anteroposteriorly 

 by 9.8 for the greatest diameter. 



MEASUREMENTS IN MILLIMETERS OF LOWER TEETH IN SPECTMENS OF 



Plasiadapis cookei 



U.S.N.M. U.S.N.M. 



No. 16698 No. 2078s 



P», anteroposterior diameter : transverse diameter... 5-2: 3-7 



P«, anteroposterior diameter 5.3 



Ml, anteroposterior diameter : transverse diameter of 



talonid 6.1 : 5-6 



Mj, anteroposterior diameter : transverse diameter of 



talonid 6.4 : 5.5 6.4 : 6.3 



Ma, anteroposterior diameter : transverse diameter of 



trigonid lo.S" : . . . lo.o" : 6.2 



" Approximate. 



PLESIADAPIS? PEARCEI,2 new species 

 Plate I, figure 9 



Type.— Right ramus of mandible (U.S.N.M. No. 20787), with Mi 

 and M2. 



Horizon and locality. — Buckman Hollow Clarkforkian Paleocene 

 on La Barge Creek, NW^NE:^ sec. 12, T.26 N., R.114 W., Lincoln 

 County, Wyo. 



Specific characters. — Size close to that of Plesiadapis dubius, but 

 trigonids of lower molars narrower and talonids wider than in that 

 species. Apices of cusps on trigonid more widely spaced transversely 

 and entoconid of Mi and M2 distinctly more posterolingual in position. 



Discussion. — The two lower jaw portions considered to represent 

 this peculiarly distinctive form were at first allocated to P. rubeyi 

 but their smaller size coupled with the lingually and backward- jutting 

 entoconid position apparently precludes this possibility. The position 

 of the entoconid gives the talonid of the first two lower molars a 

 relatively marked width in contrast with the narrow trigonid, com- 



2 Named for Franklin L. Pearce who found the type specimen. 



