98 BULLETIN 169, UNITED STATES NATIONAL MUSEUM 



The principal numerical data on this form are as follows: 

 Table 16. — Measurements of ?Ptilodus sinclairi: Continuous variates 



Table 17. — Distributions of discontinuous variates: ?Ptilodus sinclairi 



Serrations P4:. 



External cusps Mi:. 



10. 

 11. 



113- 

 6. 



Internal cusps Mi: 4 7 



External cusps M2: 4 3 



Internal cusps M2: 2 3 



[7.. ..4 



Table 18. — Measurements of individual specimens of ?PtiIodus sinclairi 



These four best specimens include practically all the extremes in 

 these characters. 



A P4 collected by A. C. Silberling on January 21, 1903, now in the 

 Princeton University collection, measures 3.0 mm in length and has 

 12 clear serrations and 1 obscure. It is indistinguishable in any way 

 from some of the smaller variants of Ptilodus sinclairi from the Gidley 

 Quarry and is referred to that species. Nothing like it has been dis- 

 covered at a Lower Paleocene horizon, nor is it exactly matched in 

 any of the many Lance specimens (Cimolomys, sensu lato) known to 

 me. It bears the horizon designation "Puerco" (by which was then 

 meant approximately the series later called Fort Union No. 1), the 

 number 14, and the locality ''Moen and Beck" (a very general locality 

 including a large area along Bear Butte). Mr. Silberling informs me 

 positively that this is from Loc. 65, and this can be taken as correct. 

 The specimen is thus the oldest mammal ever found in this field. 



