NEW PALEOCENE MAMMALS SIMPSON 233 



Diagnosis. — Dentition basically arctocyonid and resembling Proto- 

 gonodon and Claenodon. Distinct, small hypocone on M^~^ (at least), 

 cingula almost completely circling these teeth. Small but well- 

 defined mesostyle present. Parastyle of M^ a distinct, strongly 

 projecting cusp. Lower molars with trigonid only slightly higher 

 than talonid, metaconid smaller than but as high as protoconid. 

 Paraconid very small, subconical, on anterior slope of metaconid. 

 Talonid basin open with continuous crescentic lophid differentiated 

 into three apices. Enamel wrinkled, but little or no tendency to 

 form accessory cuspules. 



DEUTEROGONODON MONTANUS Gidley, new species, es ms.2' 



Type. — U.S.N.M. no. 6160, part of right maxilla with M^ com- 

 plete and broken M^~^, and left lower jaw fragment with talonid of 

 Ml and most of M2. If these should prove not to be of one individual, 

 the upper jaw is to be taken as type and the lower as a paratype. 

 Collected by A. C. Silberling. 



Paratype. — U.S.N.M. no. 6161, isolated right Mg. 



Horizon and locality. — Locality 25, about 400 feet below Gidley 

 Quarry, Fort Union, Middle Paleocene horizon, Crazy Mountain 

 Field, Mont. 



Diagnosis. — Gidley: "Somewhat larger than P. [Protogonodon] 

 pentacus (Cope)." 



Simpson: Sole known species of genus as defined above. M^ 

 median width 14.6 mm. M^ length 10 mm. M2 (paratype) width 

 10.5 mm, length 12.6 mm. 



The following new genus is in several ways transitional between 

 the so-called arctocyonine and oxyclaenine creodonts. It helps to 

 emphasize the fact that a separation of more than subfamily rank, 

 at most, is unjustified between these two groups. Among the smaller 

 and more strictly carnivorous forms, the oxyclaenines proper, there 

 are two new sharply distinct species of Chriacus, two new genera 

 probably allied to Chriacus, and a species related to Tricentes and 

 tentatively retained in that genus but so distinctive that it may be 

 necessary to create another genus for it when it is better known. 



PROTHKYPTACODON,25 new genus 



Type. — Prothryptacodon furens, new species. 

 Distribution. — Middle Paleocene, Fort Union, Mont. 

 Diagnosis. — Canine semiprocumbent, root extending beneath pre- 

 molars (as in Thryptacodo7i) . Pi_2 spaced widely. P4 similar to 



" Dr. Gidley 's notes contain two drafts of a description of this species, in both of which it is refened to 

 Protogonodon. On one the words "new genus" have later been written under "Protogonodon," but there 

 is no generic name or diagnosis. Dr. Gidley thus recognized both genus and species as new, but only the 

 latter can be published as by him. 



2' Hpo, before +Thryj:tacodon. 



