494 SINCLAIR— ENTELODONTS FROM THE 



Pelonax hathrodon (Marsh) Peterson.^^ 

 Scaptohyiis altidens gen. et sp. nov. 

 Unnamed form a. 

 Unnamed form b. 



It will be noticed at once that Archceotherium is not listed from 

 the Protoceras beds. Whether it is really absent or merely lacking 

 from the collections so far examined is uncertain, nor is it yet pos- 

 sible to say to what extent the species listed from the Titanotherium 

 and Oreodon beds respectively are confined to these levels. A. 

 wanlessi, A. inortoni and A. crassum? are found in the zone of rusty 

 nodules in the upper part of the " turtle-oreodon layer " of the 

 lower Oreodon beds, and were certainly contemporary. 



The origin of the group as a whole is uncertain. The Eocene 

 achaenodonts, as Professor Osborn points out,^® are too specialized in 

 the teeth to be regarded as directly ancestral. The European genus 

 Entelodon and the American ArchceotJierium both appear in the 

 lower Oligocene, and, as Professor Osborn suggests, may have 

 sprung alike from an unknown northern or Holarctic form. A sig- 

 nificant fact bearing on this general subject is the sudden appear- 

 ance in the Protoceras beds of several types of entelodonts, both 

 large and small, in which the shape of the fourth upper premolar 

 agrees more closely with the character of that tooth in the European 

 genus than in ArchcFotherium: Perhaps this is to be explained as a 

 new faunal invasion. Mcgachcurus zygomaticus, the small form 

 which I have not named, and a still larger individual represented in 

 the Princeton collection by some teeth and other fragments, all show 

 this character. On the other hand, Megachccrus latidens Troxell 

 and Scaptohyiis altidens gen. et sp. nov. have the anterior border of 

 the tooth in question indented, as in Archceotherlnin. Further dis- 

 cussion of the affinities of entelodonts in general and the forms from 

 the Protoceras beds in particular may be postponed until the collec- 

 tion of the American Museum of Natural History has been studied. 

 This contains excellent material of one or more undescribed large 



15 Protoceras sandstones? Big Badlands of South Dakota, Peterson, 

 loc. cit, pp. 57, 58. 

 18 " The Age of Mammals," pp. 217, 218. 



