28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



T. antiqiius material exhibiting M3. A slightly more posteriorward 

 position for the hypoconulid is indicated also for Mi, somewhat remi- 

 niscent of Chriacus, though not nearly so distinctive in this respect 

 and, of course, the teeth in general are not nearly so high cusped. 



MEASUREMENTS IN MILLIMETERS OF TEETH IN SPECIMEN REFERRED TO 



Thryptacodon australis simpson, u. of wyo. no. 1076 



P4, anteroposterior diameter : greatest transverse diameter 5.1:2.9 



Ml, anteroposterior diameter : greatest transverse diameter 6.7 : 4.6 



M3, anteroposterior diameter : greatest transverse diameter 7-1:5.3 



THRYPTACODON DEMARI.o new species 

 Plate 6, figures 2, 3 



Type.— Right ramus of mandible with P1-M3, U.S.N.M. No. 20985. 



Horizon and locality. — Bison basin Tiffanian, ledge locality at south 

 rim of Bison basin, W^ sec. 28, T. 27 N., R. 95 W., Fremont County, 

 Wyo. 



Specific characters. — Size a little smaller than Thryptacodon aus- 

 tralis. P2 isolated by longer diastemata. Metaconid of P4 much bet- 

 ter developed. Proportions of Mi about as in T. australis but pos- 

 terior molars comparatively short and broad. Hypoconulid of M3 

 variable but may be much reduced. 



Discussion. — About 11 specimens in the National Museum col- 

 lections and one or two in the collection made by the University of 

 Wyoming are recognized as pertaining to the new species Thryptaco- 

 don demari. The lower molar series of this form is only a little shorter 

 than in Thryptacodon australis Simpson from the Tififany beds of 

 Colorado, and on the basis of size alone would probably not be dis- 

 tinct from that species. In many respects T. demari shows points of 

 resemblance to the distinctly more robust appearing T. antiquus. 

 The lower premolars, though slender, are well spaced anteriorly, more 

 as in T. antiquus. P4, however, has a better developed metaconid than 

 in either of these. Mi is about the same size as in more nearly con- 

 temporary T. australis, but Mo and M3 are shorter and relatively 

 broader. In M.) the shortness may be effected largely by the more 

 reduced hypoconulid in some specimens which, somewhat as illus- 

 trated by Matthew for the type of T. antiquus, may be more closely 

 joined to the entoconid, and the talonid basin opened posteriorly be- 

 tween the hypoconid and entoconid. In the Bison basin specimen 

 thought to represent T. australis, and as evident in Simpson's illustra- 



^ Named for Robert DeMar, who aided materially in the collecting of 1953. 



