478 SINCLAIR— ENTELODONTS FROM THE 



A. niortoni is represented by a larger number of specimens than 

 any other entelodont in the Oreodon beds, especially in the zone of 

 rusty caliche nodules in the upper part of the " red layer," from 

 which came all the specimens of this species collected by the Prince- 

 ton 1920 Expedition. Probably it will also be found to range down 

 into the Titanotherium beds, but has not been identified with cer- 

 tainty in the Princeton collections from that horizon. Apparently it 

 does not occur in the Protoceras beds. 



Lower Jaws. 



That there were at least two entelodonts of large size in the 

 present area of the Big Badlands during the deposition of the 

 " turtle-oreodon layer " of the lower Oreodon beds is shown by two 

 lower jaws secured by the Princeton 1920 Expedition in the valley 

 of Indian Creek in Pennington County. The larger of these, No. 

 12550, retains the mental processes and agrees so closely in size and 

 configuration of the jaw with the type of A. wanlessi that I do not 

 hesitate to refer it to that species. The incisors, tips of the canines 

 and crowns of p3 have been lost, but otherwise the dental series is 

 complete (Fig. 9). The first premolar, measuring 21 mm. antero- 



FiG. 9. Archcrotherium wanlessi sp. nov. No. 12550. Crown view of the 

 lower teeth of the left side, one third the natural size. 



posteriorly, is double-rooted, but the roots are so close together that 

 the empty alveolus would probably be indistinguishable from that of 

 a single-rooted tooth. The anterior premolars are not as widely 

 spaced as in the type (c-pi, 6.75 mm.; pi-p2, 6.75 mm.; p2-p3, 

 5 mm.). P2 is a stout tooth with slight anterior and posterior 

 cingula and a blunt cutting edge front and rear. P4 has a broad 

 mammillated heel narrowing posteriorly and a strong anterior cingu- 

 lum. The most peculiar feature of all is the presence of a single 

 cusp, the hypoconid, on the talonid of m3, internal to which there 

 is a mammillated cingulum-like edge with hypoconulid and entoconid 



