NEW PALEOCENE MAMMALS SIMPSON 229 



EMPERODON,>5 new genus 



Type. — Emperodon acmeodontoides, new species. 



Distribution. — Middle Paleoceiie, Fort Union, Mont. 



Diagnosis. — P4 with distinct, subequal paraconid and nietaconid, a 

 deep vertical posterior groove between the latter and the posterior 

 crest from the protoconid, the latter crest with a vaguely cusplike 

 swelling (smaller tiian in Acmeodon), external wall of protoconid 

 concave vertically, talonid bicuspid. Molars leptictid, cf. Prodiaco- 

 don, but paraconids relatively large and internal, cf. Acineodon. 



EMPERODOxN ACMEODONTOIDES," new species 



Type. — U.S.N.M. no. 9850, right lower jaw with P4, Mo, and 

 part of Pg. Collected by A. C. Silberling. 



Horizon and locality. — Gidley Quarry, Fort Union, Middle Paleo- 

 cene horizon. Crazy Mountain Field, Mont. 



Diagnosis. — Sole known species of genus. P4 (type) length 2.8 mm^ 

 width 1.9 mm. M2 (type and one referred specimen) length 2.9-3 

 mm, width 2.2-2.3 mm. M3 (referred specimen) length 2.9 mm., 

 width 1.9 mm. 



Family NYCTITHERIIDAE 



Although very distinct from any other known genus, the following^ 

 form is more conveniently placed in this family than any other. 



STILPNODON," new genus 



Type. — Stilpnodon simplicidens, new species. 



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



Diagnosis. — P4 with very high, slender main cusp, minute rudimen- 

 tary anterior basal cuspule, no metaconid, simple nonbasined talonid 

 with one cuspule. M3 reduced, distinct, low, nearl}^ median para- 

 conid, trigonid erect and moderately elevated above talonid, proto- 

 conid large, trigonid nearly as long as talonid, talonid short. 



STILPNODON SIMPUCIDENS,i8 new species 



Type.—V.^.^M. no. 9629, left lower jaw with P3-4, M3, and 

 alveoli. 



Horizon and locality. — Gidley Quarry, Fort Union, Middle Paleo- 

 cene horizon. Crazy Mountain Field, Mont. 



Diagnosis. — Sole known species of genus. P4 length 1 mm. Ma 

 length 1.2 mm. 



11 'Eahttjpoi, deformed +6iovt, tooth. From its peculiar P4. 

 '• AcmeodonU) + -oides, from its resemblance to Acmeodon. 

 " ZtiXttcoj, glistening +65oi)i, tooth. 

 '• Siinplej, simple + dens, tooth. From the simple P4. 



12697—35- 



