122 BULLETIN 169, UNITED STATES NATIONAL MUSEUM 



Genus BESSOECETOR Simpson 



Bessoecetor Simpson, 1936b, p. 9. 



Type. — Bessoecetor thomsoni Simpson. 



Distribution. — Middle and Upper Paleocene, Fort Union, Montana. 



This genus was based on an unusually good suite of specimens from 

 the Scarritt Quarry. It is evidently very closely allied to Palaeosinopa 

 but seems to be slightly more primitive in several respects. The 

 species Palaeosinopa diluculi, previously recorded from the present 

 fauna (Simpson, 1935d, p. 230) appears to be more nearly related to 

 Bessoecetor and may be provisionally placed in that genus, although it 

 is too poorly known to reveal all the desired generic characters. Most 

 of the characters in which it differs from Lower Eocene species of Pal- 

 aeosinopa and which were therefore given as specific characters in the 

 original diagnosis are now shown by the fine material of Bessoecetor 



Figure 20.— Bessoecetor diluculi (Simpson), U.S.N.M. no. 9810, with parts in outline added from U.S.N.M. 

 nos. 9312 and 9539, left lower jaw: a. Crown view; 6, internal view. Three times natural size. 



thomsoni to be generic characters of Bessoecetor. Tliis includes, most 

 notably, the strongly trenchant P4 with large anterior basal cusp and 

 incipient basining of talonid, the relatively small expansion of the 

 hypocone shelves, and the less reduced M^. The Middle Paleocene 

 form also has the sharply distinguished molar talonid cusps character- 

 istic of Bessoecetor. 



BESSOECETOR DILUCULI (Simpson) 



Figures 20, 21 

 Palaeosinopa diluculi Simpson, 1935d, p. 230. 



Type.— U.S.N.M. no. 9810, left lower jaw with P4-M2. Collected 

 by A. C. Silberling. 



Paratype. — U.S.N.M. no. 9553, left upper jaw with P^'-M^ (some- 

 what broken). Collected by A. C. Silberling. 



Horizon and locality. — Gidley and Silberling Quarries, Fort Union, 

 Middle Paleocene horizon, Crazy Alountain Field, Mont. 



