FORT UNIOJs^ OF CRAZY MOUNTAIN FIELD, MONT. 151 



this crest on P2. The posterior crest is less curved and is only slightly 

 external to the midline, the tooth being much more swollen external 

 to it than is Po. The heel is more definite, much wider, the cusp less 

 external, and the ridge less sloping. 



P4 is much longer and wider and somewhat higher than P2, shorter, 

 slightly narrower and somewhat higher than Mi. Aside from its 

 greater size, it differs from P3 chiefly in the much stronger heel. A 

 small cusp appears at the posterointernal angle, and a ridge running 

 anteriorly from this tends to close a small basin. A minute cuspule 

 may appear about halfway up the crown on the inside of the anterior 

 edge, but this rudiment is often lacking even on unworn teeth. Simi- 

 larly, a very vague rudiment of a metaconid appears on the most 

 progressive variants (e. g., 9545) but is oftener absent. 



The molars have small trigonids and large basined heels. On Mi 

 the trigonid is well elevated and is du'ected somewhat forward, while 

 on M2_3 it is progressively lower. On Mi_2 the talonid is considerably 

 wider than the trigonid, the inner face of the tooth base being along 

 a straight anteroposterior line and the outer face strongly oblique. 

 On M3 the trigonid and anterior half of the talonid are of about equal 

 width. The enamel is nearly smooth, but on completely unworn 

 teeth the basin is somewhat wrinkled. Variable, crenulated external 

 cingula are developed on all the molars except on the third lobe of 

 M3. There are no internal cingula. 



The paraconid is present on all the molars and is anterior and 

 slightly external to the metaconid. On Mi it is definite and well 

 separated from the metaconid, although small. On M2-3 it is much 

 closer to the metaconid and is almost fused with the latter, disappearing 

 with slight wear. On Mi the metaconid is about equal to the proto- 

 conid, and on M2-3 it is higher. On all, the metaconid is internal and 

 slightly posterior to the protoconid, and the two are connected by a 

 notched crest. Another, less prominent crest runs forward and slight- 

 ly inward from the tip of the protoconid to the anteroexternal angle 

 of the tooth, then internally along the anterior rim to the paraconid, 

 enclosing a short, transverse, very shallow and small trigonid basin. 



Mi_2 have typical hypoconid and entoconid of about equal height. 

 The sharp basin rim is vaguely expanded in the hypoconulid region, 

 but no definite apex is here formed. There are no metastylids. 



The heel of M3 is very elongate, with two definite lobes each pri- 

 marily with two large cusps, one external and one internal. The pos- 

 terior, or hypoconulid, lobe may be further complicated by the incipi- 

 ent fission of one or both of its cusps, and adventitious cuspules may 

 even appear in the basin, the exact structure of this part being highly 

 variable, although its basic features, the extension of the basin into a 

 third lobe and the strongly double hypoconulid, are constant. 



119212—37 11 



