230 PROCEEDINGS OF THE NATIONAL MUSEUM vol.83 



Family PANTOLESTIDAE 



The following genus, fairly common in the quarry collections, is 

 evidently allied to Pentacodon, but the pertinence of it and Pentacodon 

 to the Pantolestidae is not well established. Another form is gener- 

 ically indistinguishable from Palaeosinopa and surely belongs in the 

 Pantolestidae, but is not closely related to Pentacodon or Aphronorus. 



APHRONORUS.is new genus 



Type. — Aphronorus fraudat or, new species. 



Distribution.- — Middle Paleocene, Fort Union, Mont. 



Diagnosis.- — Generally similar to Pentacodon. P4 wdth anterior end 

 less produced downward than in Pentacodon, talonid more distinctly 

 basined, with second cuspule more distinct. M2-3 less reduced rela- 

 tive to Ml. Trigonid of M1.2 relatively shorter and entoconids 

 relatively higher than in Pentacodon. Three talonid cusps of M3 

 more distinct. P^ wdth metacone well differentiated but smaller 

 than paracone, protoconule distinct. M' and to less degree M^ slen- 

 derer and more transverse than in Pentacodon, more leptictid in aspect. 



APHRONORUS FRAUDATOR.^o new species 



Type.— U.S. ISl.M. no. 6177, left lower jaw with P4-M3. Collected 

 by A. C. Silberiing. 



Horizon and locality. — Gidley Quarry (one specimen from Silberiing 

 Quarry), Fort Union, Middle Paleocene horizon, Crazy Mountain 

 Field, Mont. 



Diagnosis. — Sole lalo^vn species of the genus. Much smaller than 

 Pentacodon inversus. Lengths of lower teeth, in millimeters: P4 (10 

 specimens) 3.2-3.8, M^ (10 specimens) 2.8-3.1, M2 (12 specimens) 

 2.5-2.9, M3 (7 specimens) 2.6-2.9. 



Genus PALAEOSINOPA Matthew 



PALAEOSINOPA DILUCULI.21 new species 



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

 by A. C. Silberiing.. 



Parai7/;pe.— U.S. N.M. no. 9553, left upper jaw with P*-M^ (some- 

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



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

 Middle Paleocene horizon, Crazy Mountain Field, Mont. 



Diagnosis. — Much smaller than any other known species of Palaeo- 

 sinopa. P4 strongly trenchant, with large anterior basal cusp and 

 incipient basining of talonid. Molar cusps high and slender. M''^ 

 with smaller hypocones than in most advanced species. Metacone 

 of M'^ distinct. Length M^"- 6.1 mm. 



n 'hippoiv, crazy +8poi, mountain. From the locality; also in analogy with the many American fossils 

 named for mountain ranges. 



20 FraudaloT, deceiver. From its resemblances to various difTerent families (as Arctocyonidae, Leptic- 

 tidae, and Hyopsodontidae), resemblances of which the majority must be deceitful. 



2' Diluculi, of the dawn. From its great age. 



