NO. 6 PALEOCENE FAUNAS OF BISON BASIN — GAZIN 15 



Discussion. — In addition to being of smaller size than Peradectes 

 elegans, it was noted that lower molars of P. pauli show a protoconid 

 which, though higher than the paraconid and metaconid, is not so 

 much elevated with respect to these cusps. Also, the hypoconid is a 

 comparatively lower cusp. Moreover, the talonid basin is relatively 

 both a little narrower and shorter than in P. elegans and the entoconid 

 and hypoconulid a little less widely separated. 



With the distinctions between species of didelphid marsupials gen- 

 erally including little more than size so far as characters of lower 

 molars are concerned and with very limited information on the varia- 

 bility of observed structural differences in these earlier forms, con- 

 clusions as to generic identity based on lower molars are not entirely 

 satisfactory. As to whether the cited differences preclude reference 

 of P. paiili to Peradectes there is no certainty. Although the some- 

 what lower protoconid might suggest Peratherium, this is not sup- 

 ported by the more abbreviated talonids, and the entoconid is not 

 nearly so prominent. Furthermore, Peratherium has not been cer- 

 tainly recognized in pre-Eocene deposits. In the absence of any repre- 

 sentation of the upper dentition, about which on a generic level evi- 

 dence of a somewhat more satisfactory nature has been developed 

 (Simpson, 1935a), the species is assigned to Peradectes. 



MEASUREMENTS IN MILLIMETERS OF LOWER TEETH IN SPECIES OF PcradcctCS 



Peradectes elegans Peradectes pauli, n. sp. 



, ' >/ " > 



A.M.N.H. U.S.N.M. 



No. 17376 U. ofWyo. No. 20879 U.S.N.M. 



(type) No. 1 104 (type) No. 20880 



Ml, anteroposterior diameter 1.7S ... ... 1.6 



transverse diameter of trigonid 0.9 ... ... 0.7 



transverse diameter of talonid 0.95 ... ... 0.75 



M2, anteroposterior diameter 1.75 i-7 



transverse diameter of trigonid i.o i.o 



transverse diameter of talonid 1.0 1.0 



M3, anteroposterior diameter 1.75 1.7 1.55 



transverse diameter of trigonid 1.05 1.05 0.95 



transverse diameter of talonid 1.05 1.0 0.8 



Ml, anteroposterior diameter 1. 75 1.65 1.6 



transverse diameter of trigonid 0.95 0.95 0.85 



transverse diameter of talonid 0.8 0.7 0.6 



Insectivora 



LEPTICTIDAE 



Simpson (1937b) presented a logical arrangement of the earlier 

 leptictids which went far toward clarifying the complexity and di- 

 versity of these forms. Nevertheless, a review of the various mate- 



