l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



and exhibiting a slightly more noticeable paraconid and a better de- 

 veloped and more posterolingual entoconid, Paraconids of lower 

 molars higher and more lingual, but hypoconulid of Mj and M2 in- 

 distinct and less prominently projecting on M3, Entoconid on Mi and 

 M2 more forward in position. Small cuspule on crest anterolingual 

 to hypoconid on M3. 



Discussion. — The structure of P4 and the general form of the molars 

 suggest an alliance of this form with Aphr ononis and hence with the 

 pantolestids, although the weakness of the hypoconulid would seem 

 to negate such a relationship. The molars, though exhibiting com- 

 paratively acute cusps, might by themselves have been regarded as 

 condylarth. 



P4 of Bisonalveiis has a slightly better developed paraconid at the 

 anterolingual margin of tooth, and a more pronounced and postero- 

 lingually located entoconid so that this portion of the talonid crest is 

 not so depressed or so nearly oblique. The metaconid is only a little 

 lower than the protoconid and slightly posterior to it. The shape of 

 these two cusps is rather like that in Aphronorus. 



The lower molars show elevated trigonids, somewhat less so than 

 in Aphronorus, but the paraconid is almost as high as the metaconid. 

 The paraconid, moreover, is more lingual in position than it is in 

 Aphronorus. The talonids of the molars are basined much as in 

 Aphronorus, but the arcuate posterior crest of the first two shows 

 little or no evidence of a hypoconulid. It may be noted that the 

 hypoconulid on molars of Aphronorus is relatively weak in compari- 

 son with middle Eocene Pantolestes but is nevertheless clearly de- 

 fined. In Bisonalveus, furthermore, the entoconid has a more forward 

 position on the crest of the talonid in Mi and M2 than in Aphronorus. 

 In M3 the entoconid and hypoconulid are closer together. An- 

 terior to the hypoconid on M3 (only) there is a distinct cuspule, much 

 as seen in some leptictid molars. 



Bisonalveus lower molars differ from those of Bessoecetor in much 

 the same way as they do from those of Aphronorus. The fourth lower 

 premolar, however, is entirely different from that of Bessoecetor and 

 has more nearly the form of that in Aphronorus. 



BISONALVEUS BROWNI,^ new species 



Plate I, figure 5 



Type.—Leh ramus of mandible with P4-M3, U.S.N.M. No. 20928. 

 Horizon and locality. — Bison basin Tiffanian, saddle locality, south 



6 Named for Dr. Roland W. Brown. 



