138 BULLETIN 16 9, ITXITED STATES NATIONAL MUSEUM 



still lower and likewise poorly separated paraconid is almost directly 

 anterior to the protoconid but slightly more internal. The talonid is 

 wider than the trigonid and is very long. It has a crest that begins 

 rather indefinitely on the external side against the base of the trigonid 

 and curves back to the posterointernal corner of the tooth. Its 

 highest part is where it swings internally and across the midline of 

 the tooth, and here it bears two or three vague cuspules. There are 

 also two small cuspules on the inner margin of the talonid, separate 

 from the crest and at a lower level. The more definite of these is 

 just anterior to the posterointernal corner, and the other vague cusp 

 lies between this and the metaconid base. The sloping and volute 

 surface of the talonid, from the crest down to the inner margin, is 

 finely papillated and wrinkled. The lowest point of this surface is. 

 at the posterointernal corner, where there is an almost spoutlike exit 

 from the vague talonid basin. 



M2 was figured by Douglass {"Megopterna minuta"), but his draw- 

 ing makes the cusps appear more upright, sharp, and distinct than 

 they really are. The trigonid suggests that of Mi but is much les& 

 elevated, the cusps are better separated, the paraconid is more inter- 

 nal, and the trigonid is given a more quadrate form by the angulation 

 of the crest connecting protoconid and paraconid. The talonid is 

 broad and oval, less sloping and more distinctly basined than that of 

 Ml. The crest defines the posteroexternal angle, instead of curving 

 obliquely across the tooth as on Mi, and there are two distinct inter- 

 nal cusps, the more posterior of which is connected to the crest. The 

 basin surface is papillated as on Mi, 



M3 is not preserved on any specimen in the collection. From its 

 alveoH, it was smaller than M2, Upper teeth have not been recog- 

 nized. 



From the downward curvature of the low^er margin posterior to the 

 dental region, it is evident that the angle was of placental type. The 

 mental foramina are numerous and variable. There may be a cluster 

 of three or four in the general region of P4. The most constant 

 appear to be a fairly large foramen approximately between P3 and P4 

 and a smaller one about between P4 and Mi. 



The type is not well preserved, and I have not remeasured it. It 

 may be slightly larger than the other specimens, but there is no doubt 

 that all are conspecific. The most reliably measurable dimension is 

 the oblique maximum diameter of Mj, that is, a dimension in the 

 midline in a vertical (but not also a horizontal) plane, from paraconid 

 to base of posterior end of talonid. ^^ The constants of this dimen- 

 sion in the National Museum sample are: N, 8; R, 2.6-2.9; M, 

 2.71 ±0.04; a, 0.105 ±0.026; V, 3.9 ±1.0. The width of this tooth 



«6 The ordinary length, a horizontal between transverse, vertical tangential planes, would show great 

 subjective and accidental variation in such a small and peculiarly oblique tooth. 



