12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



No. 20736, but it may be moderately developed on the cingulum of 

 P* and sometimes P^ in E. oshornianum. 



The lower premolars appear relatively more slender in Ectocion 

 ralstonensis than in E. oshornianum, and P* has a less molariform 

 appearing talonid with, as noted by Granger (1915, p. 353), a much 

 weaker entoconid than usually seen in E. oshornianum ; also E. ral- 

 stonensis exhibits a shallower mandible. 



Upper and lower molars of Ectocion ralstonensis are apparently not 

 distinctive in comparison with E. oshornianum, except for the greater 

 average size in the latter. However, comparison with Gidleyina wy- 

 omingensis (Gazin, 1956) shows that, as earlier stated, the crests 

 from the protocone to the protoconule and metaconule of the upper 

 molars are better defined in the latter. Moreover, in some specimens 

 of Gidleyina wyomingensis and in the types of G. silherlingi and G. 

 superior the parastylid crest of the lower molars tends to join the 

 metaconid, suggestive of Phenacodus. As noted by Granger, the 

 parastylid crest of Ectocion, as far as observed, is separate from the 

 metaconid in the lower molars. 



MEASXTREMENTS IN MILLIMETERS OF DENTITION IN SPECIMEN OF 



Ectocion ralstonensis, u.s.n.m. no. 20736 



Length of upper dentition from anterior margin of canine (at alveolus) 



to posterior margin of M' 49.7 



Length of upper cheek tooth series, P*-M', inclusive 41.8 



Length of upper premolar series, P*-P*, inclusive 24.0 



Length of upper molar series, M*-M^ inclusive 18.0 



C, anteroposterior diameter at alveolus : transverse diameter at alveolus. 4.1 : 2.8 



P', anteroposterior diameter : transverse diameter 3.0 : 1.5 



P^ anteroposterior diameter : transverse diameter 4.0 : 2.2 



P^ anteroposterior diameter : transverse diameter 5-7 : 5-S 



P*, anteroposterior diameter : transverse diameter 6.0 : 7.3 



M\ anteroposterior diameter : transverse diameter across anterior por- 

 tion 6.2 : 8.5 



A'P, anteroposterior diameter : transverse diameter across anterior por- 

 tion 6.2 : 9.1 



M^ anteroposterior diameter : greatest transverse diameter 4-9 : 7-S 



Length of lower cheek tooth series Pi (at alveolus )-M3, inclusive 42.8 



Length of lower premolar series. Pi (at alveolus) -P4, inclusive 23.3 



Length of lower molar series, M1-M3, inclusive 20.0 



P3, anteroposterior diameter : transverse diameter 5.5 : 3.2 



Pi, anteroposterior diameter : transverse diameter 6.7 : 4.1 



Ml, anteroposterior diameter : transverse diameter of talonid 6.5 : 5.1 



M2, anteroposterior diameter : transverse diameter of trigonid 6.5 : 5.4 



Ma, anteroposterior diameter : transverse diameter of trigonid 6.7 : 4.5 



