CHALICOTHERIID^. 695 



a. External cusps of superior molars more or less conic. 

 An antero-external cingular cusp Pachynolophus. 



aa. External lobes of superior molars, inflected Vs. 

 /9. No cresceutic inner lobes. 

 No intermediate lobes ... Chalicotherium. 



The following regions have thus far furnished species of the above- 

 mentioned genera: 



Europe — Pachynolophus, Chalicotherium. 



North America — Ectocion, Leurocephalus, Palceosi/ops, Limnohyus, Lami- 

 dotherium. 



Asia — Nestoritherium. 



Of the American genera, Leurocephalus S. S. and 0. has been found by 

 the Princeton Exploring Expedition of 1877 in the Bridger formation, but I 

 have not met with it myself Ectocion Cope is known from a single species 

 found in the Wasatch formation of Wyoming. 



ECTOCION Cope. 



American Naturalist, June (May 20), 1882, p. 522. 



Superior molars supporting eight cusps, viz, two internal, two interme- 

 diate, and two principal external, together with two which arise from the 

 external cingulum — one opposite the space between the principal external 

 cusps and one at the anterior external angle of the crown. Fourth supe- 

 rior premolar with two external and one internal cusp. The inferior molars 

 supporting four alternating cusps, which are connected by oblique ridges, 

 thus forming one V and more or less of a second anterior one. Fourth 

 premolar with two posterior cusps. Third premolar with one posterior 

 cusp. Skeleton unknown. 



Until the feet of this genus are known, it will not be possible to locate 

 it with certainty. Its dental characters have considerable resemblance to 

 those of Protogonia, and should the feet have the characters of the Condyl- 

 arthra, its position will be near that genus. It is distinguished from Proto- 

 gonia by the two-lobed fourth superior premolar, and from Phenacodus by 

 the Vs of the inferior molars. 



The chai-acters of the molars are especially interesting as displaying 

 the type which no doubt gave origin to the prevalent type of the Peri^so- 



