168 BULLETIiSr 16 9, UNITED STATES NATIONAL MUSEUM 



Horizon and locality. — Loc. 13,^^ Fort Union, Upper Paleocene 

 horizon, Crazy Mountain Field, Mont. 



Diagnosis. — A poorly characterized species with M2 very low and 

 broad. Dimensions of type Ms, 3.7 by 3.6 mm.^" 



Discussion. — Gidley compared this isolated tooth in a broad way 

 to Absarokius and Tetonius, but his reference to Tetonius was clearly 

 Intended to be merely provisional. The resemblance exists, of course, 

 but is not exact, and the tooth more nearly resembles M2 of Plesiadapis, 

 which was poorly laiown to Gidley when he was working on these 

 primates. This is a more probable reference, although it cannot be 

 definitive on the basis of one tooth. The size is slightly, but signifi- 

 cantly, larger than for M2 of P. gidleyi, and the crown is slightly lower. 

 There is a closer resemblance to P. anceps of the Scarritt Quarry, but 

 the crown has a broader, blunter aspect. 



A lower incisor figured by Gidley (1923, pi. 3, fig. 13)''^ probably 

 belongs to this species. It very closely resembles the corresponding 

 tooth of P. gidleyi. 



Among the specimens found by Silberling and me at Loc. 13 in 1932 

 a,re two probably referable to this species. One is a right Mi, like 

 that of P. anceps except for its wider lower aspect and stronger external 

 cingulum. It measures 3.3 by 3.1 mm. The other is an upper incisor 

 also resembling that of P. anceps but consideral^ly heavier and wider 

 relative to its labiolingual diameter, the lateral apical cusp large and 

 directed more laterally, and with marked rugosities and small sec- 

 ondary cuspules on its lingual face. There is also a slightly smaller 

 but otherwise almost identical tooth from this locality in the Princeton 

 collection. 



When I described Plesiadapis anceps, from a lower level near Loc. 

 13, I was not aware that Tetonius rex Gidley belonged (in all prob- 

 ability) to Plesiadapis. The species may be synonymous, in which 



6' This was published as from Loc. 12 and bears that datum on the label, but it seems certain that this 

 is not the locality in sec. 30, T. 6 N., R. 15 E., which we relocated in 1932 and which Mr. Silberling then 

 noted as Loc. 12. Id the first place, he records only invertebrates, no mammals, from that locality. In 

 the second place, it is low in the Fort Union No. 3, and less than 550 feet above the Gidley Quarry, strati- 

 graphically, whereas Gidley's published and manuscript data say "nearly 4,000 feet higher in the beds than 

 in the 'Gidley Quarry' and 'Silberling Quarry' levels", which is approximately true of Locs. 11 and 13. In 

 the third place, Gidley's data give locality "No. 12" in sec. 22, T. 5 N., R. 14 E., and Loc. 13, but not 

 Silberling's Loc. 12, is in that section. Loc. 11 was formerly thought also to be in that section, but in 1932 

 it was relocated as across the line in section 23. In the fourth place, we found other material apparently 

 of the same species at Loc. 13, and at no other horizon or locality. And finally. Dr. Gidley himself seems 

 to have been in some doubt about this locality, for on a label of some other material he has noted "No. 12 

 (?13)", whereas there could hardly be any question about the distinction between the localities now recog- 

 nized as 12 and 13, since they are at widely different horizons and far from each other in the field. It seems 

 certain that the true type locality of this species is either Loc. 13 or Loc. 11 and highly probable that ic is 

 13, although this point does not matter as 11 and 13 are near each other and at the same level. 



"» Gidley gives 3.8 by 3.S mm, which is as close an agreement as is probable in measurements by different 

 workers. I have thought best in all cases to give my independent measurements, so that they are more 

 likely to be comparable throughout this paper. 



"' The figure is of the outer side of the tooth, peculiarly oriented, and is not very characteristic. The 

 legend gives 12 as its locality, but the label says "12 {?13)", and for the reasons already given I am confi- 

 dent that it is really from Loc. 13, at least as they are now numbered. 



