42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, I3I 



species of this Tiffanian genus. The genotype Litolestcs ignotus Jep- 

 sen is from the Silver Coulee horizon in the Polecat Bench series and 

 L. nofissimiis from the Melville portion of the Crazy Mountain Fort 

 Union. Litolcstes lacunatus is represented in the Bison basin collec- 

 tions by two additional specimens from the same locality as the type: 

 a lower jaw fragment with Mi and M2 (U. of Wyo. No. 1083) 

 and a jaw fragment with Ms and part of M2 (U. of Wyo. No. 1079). 

 A lower jaw portion with P3, P4, and a much worn Mi (U. of Wyo. 

 No. 1059) from the saddle locality may represent this species, but 

 P4 is lower and wider and lacks any evidence of a metaconid ; more- 

 over, the details of Mi are rather obscured by wear. A jaw fragment 

 with only P4 (U.S.N.M. No. 21017) corresponds very closely to the 

 type but came from the locality at the extreme west end of the basin. 

 A maxilla (U.S.N.M. No. 20931) from the west-end locality ex- 

 hibiting P^-M- has rather well worn molars ; nevertheless there seems 

 no doubt that it represents Litolestes lacunatus. P' and P"* are nearly 

 similar to those teeth in L. notissimus, but the parastyle, a very small 

 cusp on P^ in L. notissimus, is absent on this tooth in L. lacunatus, 

 however, that on P4 is more robust in L. lacunatus. The parastyle 

 and perhaps the metastyle on the molars are not so outstanding buc- 

 cally as in L. notissimus. Moreover, the talon portions of the molars 

 appear to be a little broader anteroposteriorly in the Bison basin 

 specimen. 



MEASUREMENTS IN MILLIMETERS OF TEETH IN SPECIMENS OF 



Litolestes lacunatus 



U.S.N.M. 



No. 3 1 01 6 



(type) 



Ft, anteroposterior diameter : greatest transverse diameter 3.2 : 1.9 



Ml, anteroposterior diameter : greatest transverse diameter 2.7:2.0 



U. of Wyo. 

 No. 1079 



Mj, transverse diameter of talonid 2.2 



Ms, anteroposterior diameter : greatest transverse diameter 2.2:1.6 



PHENACODONTIDAE 



GIDLEYINA WYOMINGENSIS, new species 

 Plate 9, figures 3, 4 



Type. — Right ramus of mandible with P3-M1, U.S.N.M. No. 20790. 



Horizon and locality. — Bison basin TifTanian, locality at west end 

 of Bison basin, N^ sec. 29, T. 27 N., R. 95 W., Fremont County, 

 Wyo. 



