NO. 6 PALEOCENE FAUNAS OF BISON BASIN — GAZIN I9 



rim of Bison basin, sec. 28, T. 27 N., R. 95 W., Fremont County, 

 Wyo. 



Specific characters. — In size of teeth Bisonalvens brozvni is dis- 

 tinctly smaller than Aphronorus jraudator Simpson. The length of 

 the lower molar series is about 13 percent shorter, whereas P4 is about 

 45 percent less in length, and 36 percent narrower. Specific characters 

 are not otherwise distinguished from those of the genus. 



In addition to the type there are in the collections of National Mu- 

 seum a fragmentary left mandibular ramus with M3 (No. 20929) and 

 an isolated P4 (No. 20930). A jaw fragment with a much worn P4 

 and Ml in the University of Wyoming collections (No. 1067) may 

 also represent this species. 



MEASUREMENTS IN MILLIMETERS OF LOWER TEETH IN TYPE SPECIMEN 



OF Bisonalveus broimii, u.s.n.m. no. 20928 



Length of lower cheek tooth series, P4-M3, incl 9.5 



Length of lower molar series, M1-M3, incl 7.5 



Pj, anteroposterior diameter : greatest transverse diameter 2.2:1.5 



Ml anteroposterior diameter : transverse diameter of trigonid 2.5: 1.7 



Ma anteroposterior diameter : transverse diameter of trigonid 2.6:2.0 



M3 anteroposterior diameter : transverse diameter of trigonid 2.6:1.5 



Primates 



PLESIADAPIDAE 



In numbers of jaws and, to a lesser extent, maxillae, the plesia- 

 dapids are surprisingly well represented. Not less than four species, 

 presumably divided between two genera, are recognized. Not all, 

 however, are found associated at any one locality. The most primi- 

 tive, Pronothodectes cf. matthewi, and presumably the most progres- 

 sive, Plesiadapis cf. fodinatiis, are not found together, but both are 

 associated with the forms or variants of the forms that might be re- 

 ferred to as intermediate in development, Pronothodectes simpsoni 

 and Plesiadapis jepseni. Pronothodectes is generally regarded as a 

 forerunner of Plesiadapis, which it undoubtedly is, but their occur- 

 rence together here is unquestionable in two restricted localities. 

 Pronothodectes cf. matthewi and a small variant of Pronothodectes 

 simpsoni are found associated with Plesiadapis jepseni at the saddle 

 locality and typical Pronothodectes simpsoni is associated with Plesia- 

 dapis jepseni and Plesiadapis cf. jodinatiis (a single specimen of a 

 small individual) at the stratigraphically much restricted ledge locality. 

 At the more westerly and probably higher localities Plesiadapis cf. 

 fodinatus is found with scant material referred, perhaps questionably, 

 to Plesiadapis jepseni. 



