20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



PRONOTHODECTES, cf. MATTHEWI Gidley, 1923 

 Plate 2, figures i, 2 



A decidedly small plesiadapid is represented in the collections by 

 four lower jaw portions and a maxillary fragment. One of the jaws, 

 U.S.N.M. No. 20758, includes P4-M2 and part of M3, and a second 

 specimen, U. of Wyo. No. 1062, exhibits P3-M1. The maxillary por- 

 tion, U. of Wyo. No. 1099, with two molars, is very tentatively re- 

 ferred but would seem to belong with this material rather than the 

 larger Pronothodectes siinpsoni. 



There is little doubt that the genus represented is Pronothodectes 

 rather than Plesiadapis, as the dental formula includes all the lower 

 premolars. The species represented is very close to the small Pro- 

 nothodectes matthewi, which Gidley (1923) described from the Mon- 

 tana Fort Union, The lower premolars and molar trigonid cusps, 

 though sloping, are less so than in Plesiadapis material of the P. anceps 

 type, and the trigonids are moderately compressed anteroposteriorly 

 as in Pronothodectes matthewi. Only a slightly greater transverse 

 width to the teeth was noted in the Bison basin material. 



All the specimens of this form were obtained from the saddle lo- 

 cality at the south rim of the Bison basin, associated with Pronotho- 

 dectes cf. simpsoni and Plesiadapis jepseni, but not the advanced 

 Plesiadapis cf. jodinatus. 



MEASUREMENTS IN MILLIMETERS OF TEETH REFERRED TO 



Pronothodectes matthczin gidley 



U. of Wyo. 

 No. 1099 



M\ anteroposterior diameter 2.5 



M", anteroposterior diameter 2.5 



U.S.N.M. U. of Wyo. 



No. 20758 No. 1062 



P3, anteroposterior diameter : transverse diameter 1.8:1.5 



P4, anteroposterior diameter : transverse diameter .... 2.1:1.7 2.2:1.8 



Ml, anteroposterior diameter : transverse diameter 



of talonid 2.4 : 2.0 2.5 : 2.1 



M2, anteroposterior diameter : transverse diameter 



of talonid 2.5 : 2.3 



Ma, anteroposterior diameter 3.2' 



» Approximate. 



PRONOTHODECTES SIMPSONI,« new species 



Plate 3 



Type. — Right ramus of mandible with P4-M3, U.S.N.M. No. 20754. 

 Horizon and locality. — Bison basin Tiffanian, ledge locality at south 



^ Named for Dr. G. G. Simpson in appreciation of his work on the early 

 primates. 



