FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 163 



every dimension. Apex with four cuspules, second highest, first three 

 anteroposterior, and fourth shghtly internah Talonid very short, 

 with one cusp. Mi with elongate trigonid, paraconid far from meta- 

 conid, no trigonid basin. IMo-s with closed trigonid basins and para- 

 conid small, near metaconid, but distinct. Talonid of M3 with well- 

 differentiated third lobe, posterointernal rim elevated and vaguely 

 including two or more apices. Protoconid reduced on M2_3. Trigonid 

 cusps all well in from the margin. 



ELPHIDOTARSIUS FLORENCAE Gidley 



Plate 10, Figures 2, 2a 

 Elphidotarsius florencae Gidley, 1923, p. 10. 



Type.— V.S.N M. no. 9411, left lower jaw with P4-M3. Collected 

 by Dr. J. W. Gidley. 



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

 horizon, Crazy Mountain Field, Mont. 



Diagnosis. — Sole known species of genus as diagnosed above. See 

 also description and measurements below\ 



Discussion. — •P4 is a very peculiar tooth, longer, wider, and liigher 

 than Ml although not greatly exceeding the latter in any dimension. 

 Both sides are almost smoothly convex, but the apex is formed by 

 four cuspules, or serrations, of which th6 second is highest although 

 the third is slightly larger. The first three are in a straight anteropos- 

 terior line, the fourth slightly more internal. The very short heel has 

 one cusp, from which a small sharp crest descends vertically along the 

 posteroexternal edge of the tooth and turns into the external cingulum. 



On Ml the distinct but small paraconid and the larger metaconid 

 are widely separated and there is no trigonid basin. The metaconid 

 is posterointernal to the protoconid. In the talonid the hypoconulid 

 cannot be distinguished and the basin is not completely closed, as 

 there is a deep narrow notch between the entoconid and the trigonid. 

 On M2 the trigonid is much shorter and wider, the metaconid less 

 posterior, the paraconid close to the metaconid although still distinct, 

 a small trigonid basin present. The talonid is like that of M 1 but larger. 

 The trigonid of M3 is like that of M2. The heel is modified by the 

 addition of a well-differentiated third lobe, the elevated posterior and 

 posterointernal rim of which shows some tendency to split into two 

 cusps, although these are not distinctly developed. On Mi the proto- 

 conid and metaconid are of nearly equal height. On M2 the protoconid 

 is slightly and on M3 decidedly lower than the metaconid 



To an even greater degree than is common in primitive mammals the 

 alveolar border slopes outward, so that the external faces of all the 

 cheek teeth are much higher than the internal. 



Presumably an enlarged incisor was present, but its root did not 

 extend under P4, and the jaw is broken oft" at this point. 



