FIG. 168. Lower jaw and teeth of Lambdotherium popotifficuni (cf. Fig. 167). The inferior 

 molars retain a vestige of the paraconid, the fourth premolar is becoming molariform. ; i. 



FIG. 169. Lower premolars of an undescribed species of the family TitanotheriidiB, Dinta Formation, 

 Upper Eocene, showing progressive molarization of 2h'P+ X j|. 



ms 



m.r 



tip. i 



.mts 



"ml 



Fio. 170. Upper milk molars <ij> 1 - >'/<-!, and first permanent molar of a primitive Middle 

 Eocene Titanothere (Palceosyops major). The external cusps are becoming crescentic, producing a 

 bunoselenodont type ; the primitively triangular arrangement of the three main cusps is still 

 evident. The fourth milk molar is seen to be closely similar to the first permanent molar. The 

 cusps of the milk molar are lettered in accordance with Scott's premolar nomenclature (see pages 

 195-200), but it is probable that the cusp marked te in rlp3 corresponds to the postero-internal 

 cusp of dp 2 and the aiitero -internal cusp (dc) of i!pl, as in the Equidte (cf. Fig. 166). Unlike the 

 Equidse the Titanotheres have greatly reduced the proto- and metaconules of the molars, x ^-. 



FIG. 171. Upper dentition of a specialized Oligoceue Titanothere (Brontotherium tichoarus). 

 The molars are now quadrate, the outer cusps sharply V-shaped, x J. 



