696 THE WASATCH FAUlirA. 



dadyle dentition, and demonstrates the correctness of the position which I 

 assumed in the year 1874 on this subject. This was, in brief, that the lopho- 

 dont type of molar has been derived from the bunodont by confluence of 

 tubercles. In the family of the ClialicotlieriidcE the genus Pachynolophus 

 exhibits the transverse cross-crests and external Vs characteristic of so many 

 genera of the order. In Lamhdotherium these crests are partly broken up, 

 and in Palceosyops entirely so. In all of these genera the external Vs are 

 complete, though little indented in FachynoIojyJius. But in Edocion these 

 also are broken up into a median cusjj representing the apex, and a lateral 

 external one, which corresponds with the jjrominent lateral edge of the V. 

 A. little confluence of these elements will give the type of Lambdotherium. 

 Were the median external marginal cusps wanting, the superior molars 

 would be much like those of Hyracotherium, with less tendency to confluence 

 of the median cusps than in most of the species of that genus. The supe- 

 rior molars are also much like those of Acoessvs, but the premolars are 

 different. ' 



But one species is known to me — 



ECTOCION OSBORNIANUM Cope. 



Oligoiomua osbomianug Cope, Paleontological Bulletin No. 34, 1881, December 20, p. 182. 



Plate XXVe; figs. ^10. 



The true molars of both maxillary bones, with the fourth premolar of 

 one side, are preserved more or less perfectly, with four inferior molars on 

 two fragments of the lower jaw. 



The external tubercles of the superior molars are nearly erect, and 

 have a lenticular section. The rib which separates their external faces is 

 prominent, and terminates in a free apex. The base of each face is marked 

 by a strong cingulum, but the posterior one is very short. There is a 

 strong anterior basal cingulum, but no posterior or internal one. The ante- 

 rior inner tubercle is larger than the posterior. The intermediate tubercles 

 are subround, and are anterior to the transverse line of the interior ones. 

 They do not join the latter, excepting after very considerable wear. The 

 external anterior cingular cusp is rather more prominent on the first than 

 on the second true molar. The fourth superior premolar has a well-marked 

 external anterior cingular cusp, which is, however, low; and there is no 



