l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



teeth a distinctly more molariform appearance. Resemblance is im- 

 mediately seen to the earlier Hclaletcs nanus (genotype) which in a 

 similar way is distinguished from Helaletes boops. Washakie D. 

 guyotii is a much larger form than Helaletes nanus, but D. woodi is 

 nearly intermediate. Certain of the larger Bridger individuals with 

 progressive premolars, referred to H. nanus, make a close approach to 

 D. woodi in size but the separation of the lingual cusps of P^ and P* 

 in any case is clearly not so well effected. 



Resemblance of Desmatotherium upper teeth to those of Colodon 

 is perhaps even more striking ; nevertheless, Colodon can with little 

 doubt be defended as distinct from Desmatotherium. The premolars 

 of Colodon, particularly P-, would appear to be more progressive and, 

 as shown in illustrations given by Scott (1941, pi. 81) of Colodon occi- 

 dentalis, the posterior upper premolars, noticeably P^, would appear 

 to have better defined, more clearly separated, transverse lophs. More- 

 over, a comparison of measurements shows that although D. guyotii 

 is comparable to Colodon oecidentalis in size, the latter has distinctly 

 wider teeth both in the premolar and molar series. This is perhaps 

 most noticeable in the appearance of the posterior loph of the anterior 

 molars which is decidedly longer in the illustration of Colodon. 



Lower teeth of Desmatotherium are rather poorly represented, 

 except in the Sage Creek collections. They are not known for D. 

 guyotii and only certain isolated teeth and tooth fragments are included 

 in the materials of D. zvoodi. Characters of the lower teeth of D. kayi 

 were briefly discussed by Hough but somewhat further description, 

 particularly a comparison with the earlier Helaletes, seems indicated. 



Lower premolars of Desmatotherium in comparison with those of 

 Helaletes are noticeably shortened anteriorly and relatively broad. 

 Particularly significant is the distinctly larger entoconid which in 

 Colodon is quite as large as the hypoconid. There is little evidence for 

 an entoconid in lower premolars of Hyrachyus. The progressive de- 

 velopment of the entoconid toward Colodon, and shortening of the 

 trigonid, give the premolars a more molariform appearance, but the 

 entoconid remains distinct from the hypoconid so that a completely 

 lophoid posterior crest as in the molars is never reached. 



The lower molars of D. kayi, as in Helaletes and unlike Hyrachyus, 

 show clear-cut transverse lophs with only a very subdued crista be- 

 tween them, a tooth form already realized in Heptodon. The para- 

 stylid, particularly on M3, seems more reduced in Desmatotherium 

 than in Helaletes and much more reduced than in Hyrachyus. The 

 hypoconulid on IMa may be slightly more reduced than in either 

 Helaletes or Colodon. The lower molars of Colodon, in addition to 



