418 PROCEEDINGS OF THE ACADEMY OF [1892. 



distinct element. In AnaptoynorpJnis of the Wasatch and Bridger 

 the lower premolars are as simple as in Mixodedes, but the upper 

 ones have added a deuterocone, which is particularly well developed 

 in p*. The type of j^remolar structure which is most prevalent among 

 the Eocene mesodonts is exemplified by Hyoprndua, a genus which 

 is very abundantly represented in the Wasatch, Bridger and Uinta 

 formations. In this genus the number of the premolars is still 

 unreduced, being |; the anterior members of the series are of small 

 size and perfectly simple, but the posterior two in each jaw have 

 added new elements. In the upper jaw P3 ^^^ i have a crown trans- 

 versely placed, consisting of a trenchant pyramidal protocone and a 

 smaller but well developed deuterocone. In the lower jaw p^ has in 

 addition to the protoconid only a rudimentary metaconid, forming 

 an inconspicuous heel ; in p* this heel is better developed, and on or at 

 the internal side of the protoconid appears a small deuteroconid. 

 In the existiug representatives of the series, there is not very much 

 advance upon the degree of premolar complication found among 

 the Eocene mesodonts. In the lemurs there is the remarkable 

 change first pointed out by Schlosser (No. 10) that the most anterior 

 lower premolar has assumed the form and functions of the canine, 

 but it bites behind the upper canine. In the higher primates the 

 premolar type is that of the human "bicuspid," the crown consist- 

 ing of two elements only, the protocone and deuterocone. The 

 lower teeth do not exhibit the metaconid, which, as we have seen, is 

 imperfectly develoj^ed in some of the Eocene forms. 



II. CREODONTA. 



In this group there is considerable divergence as to the amount 

 and kind of premolar development. P 1, 2 and 3 in both jaws 

 ordinarily remain quite simple, or at most complicated by the 

 addition of a small posterior basal cusp in the inferior teeth, repre- 

 senting the metaconid. Sometimes, however, these teeth become 

 very much more complicated, as in Oxycena and Palceonictis, in 

 which Pz and 3 have large and well developed deuterocones, and in 

 Ps a tritocone is added so that this tooth becomes a reduced copy 

 of the last premolar. Several other genera display a more or less 

 prominent deutei'ocone on Ps, as foj* example Deltatherium and 

 Dissacus, and in the lower jaw the metaconid may form a more or 

 less prominent talon on p^, as in the case in Dmacus, while in 

 0.^*^/ce?la these cutting talons appear on all the inferior premolars 



