FORT U^STION OF CRAZY MOUNTAIN FIELD, MONT. 



205 



MIMOTRICENTES LATIDENS (Gidley) 



Figure 54 



Tricentes latidens Gidley, Simpson, 1935d, p. 236. 



T]jpe. — U.S.N.M. no. 9269, left lower jaw with canine and P2-M3. 

 Collected by Dr. J. W. Gidley. 



Horizon and locality. — Gidley Quarry, Fort Union, Middle Paleocene 

 horizon, Crazj^ Mountain Field, Mont. 



Diagnosis. — Length: width ratio (type only): M2 1.09, M3 1.30. 

 Measui'ements given in table 44. Paraconids vestigial and trigonids 

 short. 



Discussion. — This species is Imown principally from two good 

 specimens from the Gidley Quarry, the type and U.S.N.M. no. 9276, 

 a right lower jaw with P2-M2 (M2 broken), confirming but not adding 

 to knowledge derived from the type. There are two other specimens 

 from the Gidley Quarry, probably of this species but of no value, and 

 two, also very fragmentary, from the Silberling Quarry. One of the 

 latter, U.S.N.M. no. 9672, with P4 and Mj, is smaller and less robust 

 than the type, with the paraconid of Mi more distinct, but it might be 

 a variant of this species. 



The only known upper teeth of this genus, and probably but not 

 surely this species, are M^"^ from Loc. 81, in the American Museum 

 collection. Like the lower molars, they closely resemble those of 

 Tricentes, the only clear difference, and this of doubtful value, being 

 that the internal cingulum does not circle the protocone and that on 

 M^ the external cingulum does not cross the paracone. 



Table 44. — Measurements {in mm) of the two principal Gidley Quarry specimens of 



Mimotricentes latidens 



MIMOTRICENTES ANGUSTIDENS," new species 



FlGUBE 55 



T?/2?e.— U.S.N.M. no. 9277, left lower jaw with P4-M2. Collected 

 by A. C. Silberling. 



Horizon and locality. — Type from Silberling Quarry. Referred speci- 

 mens, not identified with complete certainty, from Locs. 51 and 73. 

 Fort Union, Middle Paleocene horizon, Crazy Mountain Field, 

 Mont. 



»" Angustus, narrow+rfens, tooth. 



