208 Bulletin American Museum of Natm-al History. [Vol. XIX, 



compressed antero-posteriorly, and the constriction between 

 it and the outer cusps is more marked than in /. acutideiis. 

 The hypocone is smaller on m^ and m^, absent on m3 and 

 p4. The trittocone of p4 is smaller than in /. acutidens. 



All these distinctions are exaggerations of the differences 

 between 7. acutidens and the Leptictidae of the Oreodon Beds, 

 but none of them ally it to Palceictops, in which the molars 

 and premolars (except p^) are fully as complicated as in the 

 species of the Oreodon horizon. 



The species is named in honor of Mr. Albert Thomson of the 

 American Museum Expedition of 1902, who discovered the 

 type specimens of this as well as those of four other new 

 species described in this article. 



Comparative Measurements. 



JtH 



S o o 



.go vo 

 .i; o> o 



y o c 



dH 



U 



a!>. 



Upper molar-premolar series 



true molars and fourth pre- 

 molar 



" m' longitudinal 



" " transverse 



" m^ longitudinal 



" " transverse 



Lower molar-premolar series 



" true molars 



" m2 longitudinal 



" " transverse 



" " height 



10.4 



2.6 

 4.0 

 2.1 

 3-5 



20.0 



10. 1 

 2.7 

 2.1 

 3-7 



3.3 

 4.0 



' Measurements from Leidy's figure. 



CREODONTA. 



? Pseudopterodon minutus (Douglas). 



Hyccnodon minutus Douglas. 



No. 9623, the upper jaw of a small Creodont of the family 

 Hyaenodontidae is referred provisionally to Schlosser's genus, 

 and may be identified specifically with the lower molar on 

 which Mr. Douglas based his species '' HycBnodon" minutus. 

 This upper jaw. however, cannot be referred to HycBnodon, as 



