NO. 6 PALEOCENE FAUNAS OF BISON BASIN — GAZIN 4I 



Specific characters. — Lower molars a little smaller and relatively 

 more slender than in Protoselene opisthacus. Paraconid on M2 and M3 

 slightly lingual to midposition and distinctly isolated from both proto- 

 conid and metaconid. Talonid crest, particularly the crista obliqua, 

 lower, and basin a little shallower. 



Discussion. — A single Mi (U.S.N.M. No. 21023) is known in ad- 

 dition to the type and was found at the same locality. 



Protoselene'^ novissimus may not represent this genus but is much 

 closer to it than to any other known condylarth. It has elongate 

 molars approximating the selenodonty exhibited in P. opisthacus, but 

 the crests are lower and consequently the basins a little more shallow 

 appearing. The paraconid is located in about the same position, but 

 on the posterior molars is more definitely isolated from the adjacent 

 cusps. The extent to which this cusp is joined by a crest to the pro- 

 toconid, however, is variable in the Torrejon form. Mg in the type 

 specimen measures 5.4 mm. long by 3.8 mm. wide, M3 is 5.5 by 

 3.2 mm. 



The isolated Mi can be nearly matched in material of P. opisthacus 

 but in each case the trigonid and talonid basins are a little shallower 

 and the crista obliqua between the hypoconid and trigonid is a little 

 more depressed. Mi measures 5.6 mm. long by 3.6 mm. wide. 



LITOLESTES LACUNATUS.is new species 

 Plate II, figures 3, 4 



Type. — Left ramus of mandible with P4 and Mi, U.S.N.M. 

 No. 21016. 



Horizon and locality. — Bison basin Tiffanian, Titanoides locality, 

 southwestern portion of Bison basin, sec. 29, T. 27 N., R. 95 W., 

 Fremont County, Wyo. 



Specific characters. — Approximately a third larger than Liiolestcs 

 notissimus in size of lower molars and well outside the range given by 

 Simpson (1937a). Lower premolars relatively larger. P.i with small 

 anterolingual parastylid, metaconid weak and close to primary cusp, 

 and two small talonid cuspules very close together. Paraconid weak 

 or absent on M2 and M3. Metaconid and protoconid about equal on 

 Ml and M2, and metaconid higher on M3. Entoconid comparatively 

 high on all three molars. 



Discussion. — The form herein described as Litolestes lacunatus is 

 the smallest of the condylarths recognized in the Bison basin collec- 

 tions, yet it is distinctly larger than either of the previously described 



^8 Lacivnatus = hollowed out, with reference to the Bison basin. 



