NO. I LOWER EOCENE MAMMALIAN FAUNAS — GAZIN 85 



extremity of the posterior cingulum, is about the size of the proto- 

 conule and metaconule, larger than in cf. Hexacodiis pelodes but 

 smaller than in Microstis. The protocone in Antiacodon is relatively 

 larger and does not appear so forward as in either of these. The 

 relative position of the protocone apparently results from the develop- 

 ment of an anterointernal cusp at the lingual extremity of the anterior 

 cingulum, immediately anterior to the protocone. It is smaller than the 

 accessory cusps, but rather distinctive. 



It would seem from the foregoing that although the lower jaws of 

 Hexacodiis pelodes most strongly suggest Antiacodon among the 

 latter forms, with some variation in the direction of Microsus, Knight 

 upper molars thought to be of Hexacodiis are somewhat more sug- 

 gestive of Microsus, that is, if upper teeth of Antiacodon (A.M. No. 

 12043) are properly referred. Possibly a second genus is represented 

 by the Knight upper teeth, but I am more inclined to believe that 

 variation within the genus, as noted, for example, in the varied de- 

 velopment of P4 in H. pelodes, may be sufficient to accommodate an- 

 cestry for more than one of the bunodont artiodactyls of the Bridger. 

 With regard to this it may be noted that, although premolars are not 

 known, the lower molars of H. uintensis, with their somewhat longer 

 trigonids than in H. pelodes, could possibly have given rise to those 

 of Helohyus. Bridger Helohyus, in addition to greater size, differs 

 from the earlier form, so far as known, only in more inflated cusps 

 with some reduction of the posterior cingulum and its hypoconulid. 



MEASUREMENTS IN MILLIMETERS OF UPPER TEETH 



IN CF. Hexacodus pelodes 



U.S.N.M. U. of Wyo. 



No. No. 



22248 1779 



P*, anteroposterior diameter : greatest transverse 



diameter 4.3 : 4.3 



P*, anteroposterior diameter : greatest transverse 



diameter 4-i : S-i 



M\ anteroposterior diameter buccally : transverse 



diameter of anterior portion 4.2 : 4.8 



M^ anteroposterior diameter buccally : transverse 



diameter of anterior portion 4.6 : 5.8 4.7 : 5.6 



HEXACODUS UINTENSIS Gazin 

 (Plate 14, figure 5) 



A second jaw portion of Hexacodus uintensis has been found in the 

 vicinity of Fossil Butte in the Fossil Basin. The preserved M2 

 (U.S.N.M. No. 22250) corresponds almost exactly to that in the type 



