OF THE WHITE RIVER OLIGOCENE. 61 



may be noted. Princeton No. 11440 is a typical A. mortoni with a 

 large hypocone on m^ widely spaced anterior lower premolars and a 

 large hypoconulid and entoconid in the heel of m3 (Fig. 4 B). No. 

 1483, American Museum, from the Oreodon beds on Hat Creek, 

 Nebraska, has the hypocone of m^ intermediate in size between that 

 shown in Fig. 3 D and 3 F, with the spacing between the lower pre- 

 molars as follows: c-pj, 5 to 7.5 mm.; Pi-po, 11. 5 to 13 mm.; P2-P3, 

 3.5 to 4 mm. ; P3-P4, 2 mm. to contact, in contrast with c-p^, 6; pi-Po, 

 95 P2~P3» 175 p3-p4» 3-5> as shown in Fig. 4 B. In this second Hat 

 Creek specimen the heel of mg is similar to that of our No. 12624 

 (Fig. 4 A), except that the hypoconulid is a broad ledge instead of 

 being broken up into accessory cusps. In Peterson's figure'^ the spac- 

 ing of the lower premolars is as shown in our Fig. 4 B, the hypocone 

 is small and but slightly differentiated from the posterior cingulum 

 in m^, and the third lower molar has a heel similar to that shown in 

 Fig. 4 A, except for the minor cuspidation there seen. The longest 

 gap in lower premolar spacing is ordinarily between p, and pg as in 

 Fig. 4 B, but in No. 1483, American Museum, reference to the dimen- 

 sions just given will show that it is between p^ and po. All the 

 variations in molar pattern shown in Fig. 3 are strictly contempora- 

 neous, all the specimens being from the lower zone of rusty nodules 

 of the lower Oreodon beds. Whether the development of cingula, 

 rugose enamel and accessory cuspules in the teeth of entelodonts is to 

 any extent nutritionally controlled, as suggested by Nathusius's^ ob- 

 servations on domesticated pigs, is difficult to determine, but may well 

 be used with caution in establishing or defining species. 



We may next turn to the specimens in the Yale collection which 

 Mr. Troxell has named A. clavus clavus and A. clavus darhyi. Mr, 

 Peterson, in his monograph on Dinohyits,^ has regarded the first as a 

 subspecies of A. fnortoni, and I have elsewhere indicated my inability 

 to distinguish between them and specimens in the Princeton collection 

 referable to A. mortoni. The material secured by our 1921 Expedi- 

 tion rather increases the difficulty in that it presents additional types 



"^ Loc. cit., pp. 48, 49, Figs. 4-6. 



*Vorstudien fiir Geschichte und Zucht der Hausthiere Zunaechst am 

 Schweineshaedel. H. von Nathiisius, Berlin, 1864. 

 " Loc. cit., p. 49. 



