434 PROCEEDINGS OF THE ACADEMY OF [1892» 



trenchant edges; a deuterocone is clearly marked only on P4, where 

 it has become crescentic in shape, while P2 ^"<^ 3 have trihedral 

 crowns, but no distinct internal element. In the lower jaw pi has 

 become much elevated and pointed, and has taken on the form and 

 function of a canine, the true canine having gone over to the inci- 

 sor series, as in the true ruminants. This disposition of pi is highly 

 characteristic of the family. The other premolars (p'^ — "*) have 

 neither para- nor metaconids, but compressed, trenchant and acute 

 protoconids, upon the inner side of which low ridges inclose two 

 shallow foss?e, one anterior and the other posterior. It is difficult 

 to homologize these ridges with the elements which we have 

 described in the premolars of other groups. The later oreodonts 

 are divided into two very distinct lines, the Agi'iochoerince and the Ore- 

 odontincp. In the former subfamily the White River genus Agrio- 

 choeruy displays an unusual degree of premolar complication for an 

 arliodactyl. In the upper series the anterior three teeth are very sim- 

 ple and the external surface of the protocone is convex or flattened, 

 but £3 has a small deuterocone which is somewhat back of the mid- 

 dle. 1^4 is almost molariform ; the tritocone is somewhat smaller 

 than the protocone and both are concave on the outer side, though 

 somewhat less so than the molars. The tetartocone is a mere rudi- 

 ment. In the lower jaw pi is, as in the other members of the family, 

 like a canine in form and function ; p'^and^ are simple compressed 

 cones, while p^ has all the elements of a molar and consists of two 

 pairs of crescents ; the anterior pair is made up of the proto- and 

 deuteroconids, and the posterior pair of the meta- and tetartoconids. 

 In one respect, however, this tooth is different from a molar, in that 

 the deuteroconid retains its conical shape and in consequence the 

 anterior valley opens inward in front of it, whereas, in the molar 

 the metaconid, which occupies an analogous position, is compressed 

 and flattened and by its extension forward encloses the valley com- 

 pletely. P^ of Agriochceriis is much like the curious molars of 

 LopJiiotneryx. 



In the Oi-eodontince the premolars develop in somewhat difierent 

 fashion. I\ is like that of the true ruminants and has a single pair 

 of crescents, the deuterocone having a completely crescentic shape. 

 The anterior premolars, when seen from the outside, appear to be 

 perfectly simple and trenchant, but the inner side of the crown has 

 a number of ridges disposed as loops and festoons, and which seem 

 to stand in no very definite relation to the premolar elements here- 



