24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, I3I 



A small part of this collection, that secured by Dr. Roland Brown 

 and others, was originally cataloged and described by me in a prelimi- 

 nary unpublished manuscript, as well as in a report to the U. S. Geo- 

 logical Survey, as representing Plesiadapis anceps, which it most 

 nearly resembles in the general structure of the lower molars. The 

 resemblance is noticeable in the relative breadth of the teeth and 

 strongly sloping outer walls, a feature also noted in the larger Plesia- 

 dapis rex. The protoconid in particular has a long posterolateral slope 

 quite unlike P. gidleyi and P. jodinatus or the later P. dubius and 

 P. rubeyi. This slope is characteristic of the posterolateral wall of 

 the primary cusp in premolars as well as in the molars of P. jepseni 

 and P. anceps. Plesiadapis jepseni is unlike P. anceps and more nearly 

 resembles P. gidleyi in the expansion of the posterior portions of the 

 third upper and lower molars. The posterolingual portion of M^, 

 though somewhat more expanded than in P. anceps, is possibly not 

 so distinctive in this respect as P. gidleyi; however, the third lobe or 

 hypoconulid portion of M3 is generally as much expanded as in P. gid- 

 leyi. Moreover, in about eight of the lower jaws in which the presence 

 or absence of P2 can be determined, it is certainly missing in only 

 one. This tooth is apparently not present in P. anceps, typical 

 P. fodinatus, and later plesiadapids. 



MEASUREMENTS IN MILLIMETERS OF TEETH IN SPECIMENS OF 



Plesiadapis jepseni 



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



No. 20781 No. 20780 



Length of cheek tooth series, P*-M' 12.4 



Length of upper molar series, M^-M* 8.5 



P', anteroposterior diameter : greatest transverse 



diameter 2.0 : 2.3 2.1 : 2.5 



P*, anteroposterior diameter : greatest transverse 



diameter 2.2 : 3.1 2.3 : 3.1 



AP, anteroposterior diameter : greatest transverse 



diameter 2.9 : 4.1 2.8 : 4.0 



M*, anteroposterior diameter : greatest transverse 



diameter 3-0 : 4.7 3.0 : 4.6 



M', anteroposterior diameter : greatest transverse 



diameter 2.9 : 3.9 



U.S.N.M. 



No. 20760 U.S.N.M. 



(type) No. 20586 



Length of cheek tooth series, Pi-Ms 12.6 



Length of lower molar series, Mi-AL 10.4 



Pa, anteroposterior diameter : greatest transverse 



diameter 2.4 : 1.9 



P«, anteroposterior diameter : greatest transverse 



diameter 2.4 : 2.8 2.5 : 2.4 



