CEEODONTA. 26i> 



The dental characters of the species included in this genus, so far as 

 they are known, are identical with those of Didelphys, and authors have 

 generally regarded the name as a synonym of the latter. Species are 

 numerous in the Upper Eocene of France and in the White River beds of 

 the United States. I retain Aj-mard's name provisionally, until the number 

 of superior incisor teeth of the species concerned is known. The Leptic- 

 tidce that are known, do not have so many of these teeth as does Didelphys^ 

 there being only two in LepUctis (fide Leidy) and three in Ictops {hicuspis) 

 on each side. The genus Leptictis is quite near this one, as is also Ictops. 

 The reduction of the anterior inferior cusp of the inferior molars, already 

 seen in the latter, is carried nearly to extinction in Diacodon. 



Only one, a small species of this genus, has yet been found in the 

 Eocene beds of North America. 



Pekatherium comstocki Cope. 



Plate XXV (I, fig. 15. 



Portions of the mandibles of two individuals of this species were found 

 by Mr. Wortman in the bad lands of the Wind River, Wyoming. They 

 indicate animals a little larger than the P. fugax Cope of the White River 

 beds of Colorado, or about equal to the cave-rat {Neotoma floridana). 



The generic characters include most of those displayed by the denti- 

 tion. The heels of the molars support an acute tubercle anterior to the 

 posterior border, and their external angles are elevated and have a cres- 

 centic section. The anterior internal cusp is not quite so elevated as the 

 median internal cusp, but both are in the same longitudinal plane of the 

 jaw. The posterior internal tubercle is as high as the anterior. The 

 enamel is smooth, and there are no cingula. 



Measurements. 



M. 

 Length of two inferior molars 0063 



c (total 0037 



Diameters of first true molars < ' ' J of heel 0019 



' transverse at heel 0017 



Depth of ramus at first true molar 0048 



Dedicated to Prof. Theodore D. Comstock, of Cornell University, New 

 York, who explored the Wind River region as geologist of the expedition 

 under Captain Jones, United States Engineers. 



