14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



P. ahnietisis is much smaller than Phettacodiis p. intermedius but 

 appreciably larger than P. copei. It differs essentially from the Phena- 

 codiis primaevus group, other than in size, in better developed ex- 

 ternal styles, particularly the parastyle, and in exhibiting slightly more 

 crescentic cusps. The protocone in the upper molars, for example, is 

 united by better defined crests to the protoconule and metaconule and 

 generally with the hypocone as well. The metaconule is about on a 

 line between the metacone and hypocone, not posterior to this, as 

 frequently observed in P. primaevus, nor so forward as in Ectocion. 



P. ahniensis is significantly larger than any of the P. copei material 

 observed, and although the latter exhibits fairly prominent external 

 styles on the upper molars, the cusps, particularly the protocone, have 

 less developed crests than in P. ahniensis. Granger (191 5) noted that 

 the metaconules were weak or absent in P. copei. These are appar- 

 ently not reduced in P. ahniensis. Moreover, the upper premolars, 

 strangely enough, appear more advanced than in P. copei. P^ has a 

 well-defined and separate tritocone, described as weak in P. copei, and 

 this tooth in P. almiensis also has incipient to clearly defined conules 

 and tetartocone. P* is distinctly molariform in appearance, and is 

 recognized among isolated teeth by the absence of a mesostyle and 

 by the somewhat less developed, though by no means weak, hypocone 

 (or tetartocone, in upper premolar nomenclature). Both conules are 

 present and well defined. 



Compared to earlier species, P. ahniensis is distinctly larger than 

 P. mattheivi, as well as P. gidleyi, and not nearly so robust as 

 P. grangeri among the species known from the Colorado Tiffany. 

 Moreover, the teeth are relatively not so broad transversely as in 

 P. grangeri. The premolars are decidedly more advanced than in 

 Phenacodus bisonensis. 



As noted earlier (Gazin, 1942), the teeth of P. almiensis show some 

 resemblance to Ectocion in the development of the external styles and 

 somewhat crescentic appearance of the cusps ; however, I do not 

 believe that Ectocion is represented because of the markedly elongate 

 (anteroposteriorly) and relatively narrow upper molars, the position 

 of the metaconule, and the comparatively unreduced condition of the 

 hypocone of M^. Also, in the lower molars the anterior crest joins 

 both the protoconid and metaconid, and the hypoconulid is not so 

 close to the entoconid as it usually is in Ectocion. 



