NO. 6 PALEOCENE FAUNAS OF BISON BASIN — GAZIN 39 



Ml, anteroposterior diameter : greatest transverse 



diameter 3.2 : 2.2 



Mi, anteroposterior diameter : greatest transverse 



diameter 3-6 '■ 3^- 3-3 '• ^-5 



Ms, anteroposterior diameter : greatest transverse 



diameter 3.8 : 2.6 



' Estimated. 



HAPLALETES PELICATUS,i5 new species 

 Plate 9, figure i 



Type. — Left ramus of mandible with P3-M3, U.S.N.M. No. 21008. 



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

 south rim of Bison basin, sec. 28, T. 27 N., R., 95 W., Fremont 

 County, Wyo. 



Specific characters. — Length of lower molar series about one-fifth 

 greater than that of Haplaletes disceptatrix. Premolars more inflated. 

 Metaconid of P4 weaker. Paraconid weak on Mi, vestigial or absent 

 on M2 and M3. External cingulum weak and discontinuous or absent 

 on lower molars. 



Discussion. — The type of Haplaletes pelicatus is an excellent lower 

 jaw with the cheek-tooth series in a nearly unworn state. Among 

 the referred materials are three lower- jaw fragments each with one 

 molar, all from the same locality as the type. Two of the latter are in 

 the collections of the University of Wyoming. 



The teeth in U.S.N.M, No. 21008 bear a striking resemblance to 

 those in the type of H. disceptatrix from the earlier or Torrejonian 

 equivalent of the Fort Union, particularly in the form and slope of the 

 molar cusps. The premolars, however, are a little more inflated and 

 as a consequence the metaconid of P4 is not so prominent. Haplaletes 

 is rather distinctive among condylarths, and the posterior molars, 

 particularly M3, look surprisingly like these teeth in Thryptacodon. 

 The first molars, however, bear little resemblance. 



Comparison of Haplaletes pelicatus with Haplaletes diniinutimis 

 Dorr (1952) is not feasible inasmuch as the latter is represented by 

 a partial upper dentition ; nevertheless the very small size of the Dell 

 Creek form leaves no doubt as to their distinctness. 



Measurements of teeth in H. pelicatus are included with those of 

 the following species. 



HAPLALETES SERI0R,i6 new species 

 Plate 9, figure 2 

 Type. — Left ramus of mandible with Mj and M3, U. of Wyo. 

 No. 1078. 



^'' From Greek, pelike = hasin, in allusion to the Bison basin. 

 " Serior = later, with reference to its stratigraphic position. 



