254 



BULLETIN 169, UNITED STATES NATIONAL MUSEUM 



teeth of Gidleyina montanensis are almost ideally prototypal to those 

 of Edocion, the lower teeth called W. silberlingi seem to be progressing 

 either more rapidly or in a different direction in the development of 

 P3 and the molar trigonids. This is not certain, however, as these 

 characters are highly variable and an apparent reversion of this sort 

 is not inconceivable. 



Figure Ti.—'iQidleyina silberlingi (Qidley), U.S.N.M. no. 6166, left lower jaw: a, Crown view; 6, external 

 view. One and one-half times natural size. 



P3 differs markedly from that of Tefraclaenodon in its incipient cres- 

 cent and basin, but P4 is basically similar. The molar paraconid is 

 much less distinct in ?G. silberlingi than in most specimens of Tetra- 

 claenodon, although approached by a few extreme variants of the 

 latter, and the enamel is much less rugose, the crests less crenulated. 

 These characters suggest Protoselene, but in the latter even P4 is much 

 less molariform, with the metaconid strong in ?6^. silberlingi, barely 

 incipient at best and the talonid very different. 



The following measurements are from the type: Length P3, 6.7; 

 width P3, 3.9; length P4, 7.2; width P4, 4.7; length Mi, 7.0; width 

 M„ 5.4; length M2, 7.3; width M2, 5.4; length M3, 7.3; width, M3, 4.6. 



TGIDLEYINA SUPERIOR (Simpson) 



Figure 74 



7 Tetraclaenodon superior Simpson, 1935d, p. 239. 



Type. — U.S.N.M. no. 11913, part of left lower jaw with talonid of 

 Ml, M2, and M3 still in capsule. Collected by A. C. Silberling.^^ 



Horizon and locality. — Loc. 11 or 13, about 3,000 feet above the base 

 of Fort Union No. 3, Sweetgrass County, Mont. 



Diagnosis. — Lower molars with paraconids vestigial, broad trigonid 

 basins with crenulated anterior margin, crenulations otherwise slight. 



•' The two upper molars apparently of Tetraclaenodon, discussed on a previous page, are preserved in the 

 same lot of material but are not associated with the lower jaw and were definitely excluded from the type 

 material of this species. 



