NO. 6 PALEOCENE FAUNAS OF BISON BASIN — GAZIN 35 



Depth of jaw beneath diastema between Pi and P3 31.O 



Pi, antcroi)osterior diameter : transverse diameter 3-5" : 2.2 



Ps, anteroposterior diameter at alveoH il.o 



Pi, anteroposterior diameter at alveoli 13.5 



Mi, anteroposterior diameter : transverse diameter 12.2 : 9.7 



Ms, anteroposterior diameter : transverse diameter 15.0' : 9.9 



" Approximate. 

 * Estimated. 



MESONYCHIDAE 



DISSACUS, sp. 



Mesonychid creodont material is exceedingly scarce in the Bison 

 basin collections, as only two incomplete teeth have been encountered. 

 One of these is the outer portion of an upper cheek tooth, not identi- 

 fied as to position, but showing the high conical paracone, somewhat 

 lower metacone, and a prominent parastyle characteristic principally 

 of P4-M2 in Dissactts. In size it is a trifle larger than Mg in D. nava- 

 joviiis as illustrated by Matthew (1937, figs. 16, 17). The other speci- 

 men consists of about the posterior two-thirds of a lower cheek tooth. 

 The anterior and medial portions of the protoconid, including the posi- 

 tion of a possible metaconid, are missing. The shearing talonid is 

 slightly longer than in the Torrejon D. navajovius tooth material in 

 the National Museum collections. The material, however, is not ade- 

 quate for specific diagnosis, although there would seem to be no doubt 

 as to the genus represented. 



MIACIDAE 



DIDYMICTIS, near D. TENUIS Simpson, 1935 



A lower jaw fragment with M2 and the talonid of Mi in the Uni- 

 versity of Wyoming collection (No. 1063) would appear to be the 

 only determinable miacid material so far encountered in the Bison 

 basin collecting. The specimen is from the vicinity of the saddle lo- 

 cality below the south rim of the basin. The species is clearly a minute 

 form of Didymictis and the talonid of Mi has proportions almost the 

 same as in the type of Didymictis tenuis from the Gidley quarry in 

 the Crazy Mountain Fort Union. M2 is not preserved in the D. tenuis 

 material, but the root portions shown in the type indicate a tooth 

 slightly longer than that of the Bison basin specimen. However, this 

 difference alone would not warrant recognition of a separate species. 

 Nevertheless, it is probable, in view of the difference in age of the 

 horizons represented, that the species are not the same. M2 in No. 

 1063 measures 2.6 mm. long by 1.4 mm. wide. The talonid of Mi is 

 about 1.5 mm. wide. 



