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University of California Publications. [Geology 



Butte, Crook County, Oregon. X %. 



This is evidently a true Mesocyon near the coryphaeus type, 

 possessing like that form both posterior cusp and basal tubercle 

 on P 3 . The sectorial is nearly as large as in coryphaeus. P 3 and 

 P 2 are relatively smaller. The palate is as wide posteriorly as in 

 coryphaeus, and the width between the canines is also as great, 

 but the palate of the typical coryphaeus is 15 to 20 per cent, 

 longer. There is a moderate degree of crowding of the premolars 

 anteriorly, in contrast to the open arrangement in coryphaeus 

 and josephi. The size of the brain case is relatively considerably 

 greater than in the type of coryphaeus or in a specimen of the 

 same general dimensions in our collection. M. josephi differs 

 from this form in having a longer palate, a smaller superior sec- 

 torial and first molar, and in lacking a posterior cusp on P 3 . 



