so AMERICAN MESOZOIC MAMMALIA 



passing into the curved anterior cutting edge of the tooth. The main cusp is slightly 

 recurved and there is no external cingulum. The crown is obviously that of a typical 

 pantotherian premolar. P2 is closely similar, but somewhat larger. 



Ml resembles M2 save in being slightly longer and narrower, but it is somewhat 

 worn and broken. M2 consists mainly of a single high external cusp with a convex 

 posterior and external surface and a concave internal one, the two being separated by 

 sharp anteromedian and posterointernal vertical angulations. The me'' is much smaller 

 and lower than the main cusp and is internal and slightly posterior to the apex of the 

 latter. Its separation from the base of the pr'' is imperfect and there is no trigonid basin. 

 There is no true paraconid, its place being taken by a low shelf anterior to the mc*. 

 The heel is little pronounced, sloping, not basined, with no true cusp. 



Ms is closely similar to the preceding tooth, but is a little higher, with slightly 

 more pronounced cusps, the me"* directly internal to the pr"^. M4 is lower and less slen- 

 der. The me'' is less marked and the pa'' and talonid are more nearly horizontal, but 

 the latter is markedly smaller. All the premolars and molars have two subequal fangs, 

 but on Ms the anterior root is a little the stouter. 



The dental formula assigned to this specimen by Marsh, namely I, Ci P2 M4 is 

 certainly correct. Paurodon has been cited as showing that the typical Tertiary dental 

 formula was in existence as early as the Jurassic, but the grounds for this statement are 

 difficult to see, as this formula is not that primitive for any later mammals. Neither 

 P3 M4 nor P4 M3 is the correct formula for any known pantothere, although both occur 

 among triconodonts. 



Mandible 



The horizontal ramus is remarkably short and deep. The symphysial surface is 

 large, but shorter relatively than in the dryolestids, extending back to a point beneath 

 Pi. The lower border of the ramus is slightly curved and is lowest beneath M4. The 

 internal groove is broad and shallow and converges slowly toward the lower border 

 until it is beneath Mi, then runs parallel to the lower border to the symphysis. The 

 external surface is evenly convex save where it is swollen above the root of the some- 

 what obliquely placed canine. There is one small mental foramen beneath the anterior 

 root of Pi. A small part of the coronoid was shown by Marsh, but it is now missing. 

 The anterior border of the coronoid arose some distance back of M4 at about 45° to the 

 alveolar border. In this interspace there is room for another molar, but there is no 

 trace of such a tooth although the individual appears to be adult or even old, and more 

 than four molars do not occur in any close ally of Paurodon. 



