E. L. Troxell — Entelodonts in Marsh Collection. 385 



curves strongly backward, and is placed near the canine. 

 P 2 is separated from P t by a distance of 25 mm. and from 

 P 3 by 13.6 mm. Like P^ it is rudimentary and very 

 small ; but is shorter and thicker and sits low on its roots. 

 The outer side is very convex, the inner almost flat. It is 

 strongly recurved and has cutting edges and cingula. 



P 3 is situated very close to P 4 but does not touch it. It 

 is very high on its roots, which are heavy and slope back- 

 ward. The inner side is flat, the outer convex, and the 

 two diameters have the proportion of 1 :2. A sharp ridge 

 extends from the cone to the roughened area above the 

 cingulum. 



P 4 has approximately the same antero-posterior diam- 

 eter as P 3 , but is a little thicker. It has a very low crown 

 and sits low on the roots, which point strongly backward 

 as if to exert strong pressure in that direction. The 

 heavy protoconid is also strongly recurved. The very 

 narrow but long shelf -like heel, higher in the center, joins 

 a ridge running from the point of the cone. 



M x is a much worn tooth on which an obscured talonid 

 may be seen. The entoconid is weak, the hypoconid rela- 

 tively strong, and there does not seem to be the great dis- 

 proportion in height between the anterior and posterior 

 cones seen in A. clavus claims; the anterior cones are 

 slightly wider than those posterior. 



M 2 is considerably larger than M x and appears to have 

 a double-cusped metaconid. The entoconid is small and 

 weak ; on the hypoconulid there is a small lake indicating 

 its relative prominence (cusps indicated on figs. 17, 18). 



The double-cusped metaconid of M 3 is as large as the 

 protoconid, but the entoconid is much weaker than the 

 hypoconulid or heel. 



Summary of Archceotherium marshi Group. 



A. marshi, sp. nov. : holotype, Cat. No. 12025; referred 

 specimen, Cat. No. 10290. 



In this group there are two specimens, both from South 

 Dakota. The new type is the splendid skull (figs. 10-12), 

 which has been taken for the apotype of A. crassum by all 

 writers heretofore. The chief characteristics distin- 

 guishing it from the holotype of A. crassum are: the 

 heavy zygomatic arch with the large posterior process 

 from the jugal, and its sigmoid border, which joins the 



