1 6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



rials in connection with the study of the leptictid form represented in 

 the Bison basin Paleocene has indicated the need for certain further 

 modification. 



Attention (Gazin, 1952) was called to the rather distinctive char- 

 acters observed in the type of Diacodon alticuspis, and I am now con- 

 vinced that Cope's Ictops bicuspis should not have been referred to 

 Diacodon and that Matthew's earlier disposition of this species under 

 the name Palaeictops should be revived. As well as Palaeictops bicus- 

 pis (Cope), this genus apparently should include Palaeictops tauri- 

 cinerei (Jepsen) and Palaeictops pineycnsis (Gazin) from among 

 the lower Eocene forms, and possibly also Palaeictops miniitus (Jep- 

 sen) from the Silver Coulee (Tiffanian) Paleocene. 



The genus Prodiacodon was named by Matthew as a subgenus re- 

 placing Palaeolestes (preoccupied) for the species P. puercensis of 

 the Torrejon horizon. This form, though generically distinct, is, I be- 

 lieve, more closely allied to Palaeictops bicuspis than to typical Dia- 

 codon or D. alticuspis. In 1935 Simpson (see 1937b) described Pro- 

 diacodon concordiarcensis from the upper Lebo (Torrejonian) and 

 expressed some doubt as to the correctness of referring it to that genus. 

 In view of the somewhat later but closely related form encountered in 

 the Bison basin fauna, and of the particular characteristics, rather 

 generally overlooked, of Diacodon alticuspis, I am placing both the 

 Lebo and Bison basin forms in Diacodon. These then become Dia- 

 codon concordiarcensis (Simpson) and Diacodon pearcei, new species. 



DIACODON PEARCEI,3 new species 

 Plate I, figure 6 



Type. — Left ramus of mandible with P3-M1, U.S.N.M. No. 20970. 



Horizon and locality. — Bison basin Tiffanian, small saddle below 

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

 County, Wyo. 



Specific characters. — Diacodon pearcei closely resembles Diacodon 

 concordiarcensis (Simpson) from the Crazy Mountain Fort Union 

 (upper Lebo) in the structure of the teeth, but is distinctly larger, 

 about intermediate between D. concordiarcensis and D. alticuspis. 

 P4 is seen to be about 14 percent longer and 27 percent wider than in 

 D. concordiarcensis and about 20 percent shorter and 22 percent nar- 

 rower than D. alticuspis. The paraconid of this tooth is higher than 

 in the Lebo species. 



8 Named for Franklin L. Pearce. 



