1873.] ZUI [Cope. 



premolars 2 and 3, and becomes on the true molars a longitudinal 

 cutting edge extending along the axis of the crown, not much elevated 

 above a wide base. It occupies half the length of the crown in the 

 larger molars, and is preceded by an elevated conic cusp. In front of 

 the base of this, a small conic tubercle projects forwards, which appeared 

 as a rudiment on the third premolar. The number of mandibular teeth 

 would appear to be, P. M. 3, M. 4. No portions certainly referable to 

 the superior molars were found. 



Conclusion. In summing up, it may be accepted as a result of the 

 above analysis that the genus Mesonyx represents a family of Carnivora 

 digitigrada, distinct from any now living on the globe. The form of the 

 astragalus renders it probable that the inner toe is wanting or rudimental, 

 and that there were four digits on the hind foot. The foot was also short 

 and the claws flat, and altogether without prehensile use, but rather 

 adapted for aquatic life. The number of molars exceeds that in any re- 

 cent family of Carnivora except the Protelidc, and their sectorial form al- 

 lies it at once to the extinct Ilycenodontida'. To this family the genus 

 Mesonyx may indeed be for the present referred. Among recent families 

 it approaches nearest the Canidce, but has structures borrowed from 

 others, while its numerous molars constitute a point of greater generali- 

 zation than any. Although sectorials, this character is not nearly so 

 marked as in the existing Carnivora, the cutting edge being obtuse and 

 occupying half the crown only, while the elevated cone occupying the 

 remainder distinguishes the genus from these and from Hycmodon also. 

 The lobe corresponding to this cone is preceded in Hyanodon by a 

 cutting edge, in Mesonyx by a tubercle. 



Mesonyx obtusidens. Cope. 

 Proceedings American Philosophical Soc. 1872, 460 (August 15th). 

 This species was as large as our largest wolves. While the proportions 

 of the limbs were not very different, the form was rather more slender 

 behind. The orbit was smaller, and the cheek bone more prominent 

 than in those animals. The long tail added to the general resemblance 

 to the dogs. The measurements are as follows : 



M. 



Length malar bone 0.073 



Depth " in front 016 



" "at postorbital angle 023 



" " middle of orbit 015 



Thickness " " " 013 



Transverse diameter glenoid cavity of scapula 025 



" " idnar do. for humerus 014 



Length centrum dorsal vertebra 019 



Diameter " transverse 018 



" " vertical 014 



Length centrum of a median lumbar 030 



A. p. s. — VOL. XIII. z 



