FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 197 



CHRIACUS PUGNAX Simpson 



Figure 46 

 Chriacus pugnax Simpson, 1935d, p. 235. 



Type. — U.S.N.M. no. 13782, right lower jaw with Mi_2 and alveoli. 

 Collected by A. C. Silberling and G. G. Simpson. 



Horizon and locality. — Loc. 78, Fort Union, Crazy Mountain Field, 

 Mont. 



Diagnosis. — About the size of C. pelvidens, but molars wider, tri- 

 gonids less elevated, talonids of Mi_2 notably wdder than trigonids. 

 Ml length 7.1, trigonid width 4.9, talonid width 5.9. 



Remarks. — In addition to the characters cited in the diagnosis, there 

 is a diastema anterior to P3 in the unique specimen, but the length and 

 significance of this cannot be established. The specimen is from one of 

 the lowest horizons that have yet yielded mammals in this field, only 

 200 feet above the base of the Fort Union No. 1. This suggests 

 comparison with Mimotricentes angustidens, also from a low (but not 

 such a low) horizon, but the latter is markedly smaller and otherwise 

 less ChriacusASkQ. 



Genus METACHRIACIJS Simpson 



Meiachriacus Simpson, 1935d, p. 235. 



Type. — Meiachriacus punitor Simpson. 



Distribution. — Middle Paleocene, Fort Union, Mont. 



Diagnosis. — Canine and premolars about as in Chriacus. Molar 

 trigonids lower than in Chriacus but still shearing rather than bunodont 

 (as in Tricentes). Paraconids reduced and poorly distinguished, near 

 metaconids, placed about as in Chriacus or slightly less internal. 

 Accessory cuspules developing on anterior rim of trigonid, on hypoconid 

 wings, and a slight metastyhd. Upper molars with sharp cingulum 

 around the protocone, but no protostyle. Hypocone present on M^, 

 rudimentary or indistinguishable on M^, and absent on M^. 



Remarks. — This genus is hardly distinguishable from Chriacus on 

 the basis of the premolars, which distinguish it from almost all other 

 known genera, but the molars are of quite a different adaptive type, 

 the lower crowns, blunter cusps, and prohferation of accessory cus- 

 pules in the lower molars representing convergences in varying degree 

 toward Tricentes and toward Claenodon. 



METACHRIACUS PUNITOR Simpson 



Figures 47-49 



Meiachriacus punitor Simpson, 1935d, p. 235. 



Chriacus pusillus Simpson, 1935d, p. 234. 



Type.— U.S.N.M. no. 9288, left lower jaw with Mi_3. Collected by 

 A. C. Silberling. 



