42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



In the anterior part of the small median valley a protoconule, 

 isolated from the anterior cingulum and often from the deuterocone, 

 is attached to the lingual wall of the primary cusp. The metaconule, 

 in the posterior part of this valley, as a crest may join the deutero- 

 cone and the tritocone portion of the outer wall but is usually separate 

 from the posterior cingulum or tetartocone in this tooth. 



P 4 is distinctly more molariform than P 3 - The deuterocone is 

 very large and conical, and the tritocone, while usually somewhat 

 more abbreviated than the primary cusp (paracone), is well defined. 

 The mesostyle may be fully developed but this is not invariable, as 

 in some specimens it is no more than a gentle swelling or flexure of 

 the outer wall and somewhat nearer the posterior margin than in the 

 molars. The ribs, moreover, are a little better defined than in the 

 molars. P 4 is most noticeably different from the molars in the much 

 less lingual position of the tetartocone, which appears more as a 

 cusp on the posterior cingulum, but is strongly joined to the meta- 

 conule, and the latter generally shows little or no direct union with 

 either the deuterocone or tritocone. The protoconule forms a short 

 crest parallel to the anterior crest of the primary cusp which it joins 

 posteriorly. This accessory cuspule may also be joined, but some- 

 what more weakly, by a crest from the deuterocone. The cuspule 

 on the anterior cingulum anterolateral to the deuterocone persists as 

 in the molars, as well as in P 3 . Slight plications extending into the 

 central basin from adjacent cusps and walls were noted in certain of 

 the fourth premolars, but this condition was less frequently encoun- 

 tered here than in the molars. 



The first two true molars may be discussed together as they are 

 much alike except for the greater size of M 2 . The outer walls of 

 these teeth show exceedingly well developed parastyles and meso- 

 styles, and with but feeble or no representation of ribs in the concavi- 

 ties corresponding to the outer walls of the paracone and metacone. 

 The protocone is conical but somewhat more elongate toward the 

 protoconule than is the deuterocone of P 3 and P 4 . The hypocone 

 is completely lingual in position and forms with the metaconule an 

 elongate ridge extending anteroexternally well into the central pit or 

 valley of the tooth. Also the posterior cingulum rises lingually and 

 prominently to the crest of the hypocone giving this cusp a crescentic 

 or V-shaped appearance. The anterior cingulum usually extends 

 around the base of the protocone, terminating in the valley between 

 the protocone and hypocone. It carries a prominent cuspule antero- 

 external to the protocone as observed in P 3 and P 4 . The proto- 



