ENTELODONTS FROM THE BIG BADLANDS OF SOUTH 

 DAKOTA IN THE GEOLOGICAL MUSEUM OF 

 • PRINCETON UNIVERSITY. 



Investigation aided by a Grant from the Marsh Fund of the 

 National Academy of Sciences. 



By WILLIAAI J. SINCLAIR. 



(Read April 22, 1921.) 



I had always assumed that entelodonts were rare fossils in the 

 White River Oligocene until last summer when the Princeton Expe- 

 dition to South Dakota, within an area of about two square miles in 

 the valley of Indian Creek, in Pennington County, between July 14 

 and 2y, collected five skulls and two lower jaws belonging to three 

 species of Archceotherium and noted, but refrained from collecting, 

 perhaps as many more fragmentary specimens within the same area. 

 This mass of new material made it desirable to restudy the Prince- 

 ton entelodont collection as a whole, as much of it had never been 

 adequately determined. Fortunately, the timely appearance of Mr. 

 Troxell's^ excellent paper on the entelodonts in the Marsh collection 

 at Yale greatly facilitated these studies. Whether certain of the 

 characters used in the classification of these animals are of specific 

 importance or of the nature of secondary sexual structures can not 

 yet be determined. For the present it is safer to give a separate 

 specific name to each well-defined variant, based on adequate mate- 

 rial, than to group together forms which may have been rapidly 

 mutating and thereby developing differences of the first degree of 

 importance for detailed faunal and stratigraphic studies. A review 

 of the genera and species represented follows. 



1 Am. Jour. Set., Vol. L., Nov.-Dec, 1920, pp. 243-255, 361-386, 431-445. 



467 



PROC. AMER. PHIL. SOC, VOL. LX., EE, MARCH IJ, 1922. 



