FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 



125 



root. P2 is likewise small but more elongate and with two roots. The 

 only specimen that shows Pi_2 is senile and these teeth are truncated 

 by wear at the bases of the crowns. P3 is larger than P2 but also 

 small in relation to the whole dentition. When unworn it has a 

 triangular protoconid followed by a heel with a slight interna"! basin 

 and two rudimentary posterior cusps. P4 is much enlarged and has a 

 massive protoconid, which slopes backward, and a lower distinct 

 metaconid, closely applied to the posterointernal base of the protoco- 



FiGURE 23.— AphronormfraudatoT Simpson, U.S.N.M. no. 9448, with parts in outline added from U.S.N.M. 

 DOS. 9291 and 9519, right lower jaw: a, Crown view; 6, internal view. Four times natural size. 



Figure 2i.—Aphro7iorusfraudator Simpson, U.S.N.M. no. 9560, with tooth in outline added from U.S.N.M. 

 no. 9565, left upper jaw: a. External view; 6, crown view. Four times natural size. 



nid. Anterior to this there is a sharp internal cingulum, turning into 

 a vertical crest at the anterior midline of the tooth, but there is usually 

 no paraconid or anterior cuspule, although in one or two specmiens 

 there is a slight tendency to develop a cuspule here. The large heel 

 has its main cusp external to the midline, connected by a sharp crest 

 to the middle of the trigonid base. Internal to this crest is a basin, and 

 a second, smaller and less distinct cusp is near the posterointernal 

 corner of the tooth. 



