HORSES WITH TEETH SIMILAR TO REPTILES'. 263 



turn out not to belong to the suillines. But when the evi- 

 dence of derivation drawn from other sources is considered, 

 and the geological period is taken into account, the structure 

 of the teeth is preeminently in accordance with the expecta- 

 tions of the evolutionist. It is important to notice in this con- 

 nection that Prof. Cope ventured the prediction in 1874* that 

 the quadritubercular or four-lobed bunodont f molar was the 

 primitive pattern in which the more complicated selenodont | 

 molar of the later ungulates had its origin. That this predic- 

 tion is now proved there can be no question, and the passage 

 from this simple type of tooth to the highly complicated forms 

 illustrated in this article has, I think, been close and consecu- 

 tive and intimately associated with reduction in digits. 



The Phenacodontidae present considerable variety as far as 

 their family is at present known. Prof. Cope has described 

 five genera, as follows : Phenacodus, Anacodon, Protogonia, 

 Periptych us, and Anisonchus. The first two are from the 

 Wasatch horizon, while the last three were derived from the 

 underlying Purco beds. Periptychus shows a peculiar sculp- 

 turing of the outside of the molar teeth, similar to that seen in 

 many reptiles, and is the only mammal known to possess it. 

 The molars of Anacodon lack distinct tubercles, a character 

 which assigns it the lowest position in the family. Phenacodus 

 approaches nearest to the Lophiodons in dental character and 

 is taken for illustration. As all but Phenacodus and Peripty- 

 chus are known from their teeth only, it may be necessary on 

 the discovery of the character of their feet to refer them to new 

 families. The definition of the family given by Prof. Cope is 

 as follows : Molar teeth tubercular ; molars and premolars 

 different ; five toes on all the feet.g 



MENISCOTHERIUM. 



The Meniscotheriidse has been recently established for the 

 reception of the single genus Meniscotherium, discovered by 



* Journal Academy of Natural Sciences, Philadelphia. 



t Teeth of simple structure, with short crowns and low, blunt tubercles 

 on their face. 



$ Teeth of complicated structure, with high and uniformly broadened 

 crowns, the face presenting a complex folding of the enamel plates. 



Paleontological Bulletin, No. 34, Dec., 1881, p. 178, 



