24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



more conservative and along a line independent of that for Achaeno- 

 don. Change from Helohyus has been the increase in size of the meta- 

 conule, and the shift to a more Hngual position. This is particularly 

 noticeable for IVP which, rather than having a triangular outline, has 

 achieved the quadrate form of the anterior molars with the metaconule 

 equally well developed. There is, however, no evidence of the devel- 

 opment posteriorward of M^ as in Perchoerns; nor do any of the 

 molars show development of a "pseudometaconule" anterolateral to 

 the metaconule. 



Distinction from Achaenodon is seen not only in the very much 

 smaller size of Apricidiis so far as known, but in the retention and 

 marked development of the protoconule. 



APRICULUS PRAETERITUS,8 new species 

 Plate 3, figure I 



Type.— Right maxilla with P^-M^* (teeth incomplete), U.S.N.M. 

 No. 21 100. 



Horizon and locality. — Hendry Ranch member of Tepee Trail for- 

 mation on south side of Badwater Creek, SW cor., SE^^ sec. 14, 

 T. 39 N., R. 89 W., Wind River Basin, Wyo. 



Specific characters. — Size of upper molars very close to that for 

 Helohyus plicodon. Other differences included in description of genus. 



Discussion. — The type maxilla with somewhat damaged upper teeth 

 is the only known specimen of this comparatively late survival of a 

 Helohyus-Wke dichobunid. The upper molars, though comparable in 

 size to those of Helohyus plicodon, are perhaps a little narrower trans- 

 versely, as the basal slope of the protocone and cingulum median to it 

 do not extend so far lingually. The anterointernal and posterointernal 

 portions of the molars are more nearly equal in lingual extent. 



Precise measurements of the individual teeth in the type of Apric- 

 ulus praetcritus cannot be obtained because of breakage ; nevertheless 

 over-all dimensions can be determined and the length of the pre- 

 served portion of the upper cheek tooth scries, P*-IVP inclusive, is 

 found to be 30 mm. The molar series is about 24.5 mm. long. J\P 

 is estimated to be about 8.7 (anteroposteriorly) by 10.6 mm. 



In size, upper molars of Apriculus praetcritus are only a little larger 

 than the dichobunid tooth figured by Russell and Wickenden (1933). 



8 Praetcritus, overlooked or passed over — overlooked in recent review of col- 

 lections for upi)cr Eocene artiodactyl study. 



