420 



PROCEEDINGS OF THE ACADEMY OF 



[1892. 



Sinopa, their shape and mutual relations are altogether different. 

 In Dis.iacus, the oldest genus of the family, this tooth has all the 

 elements of the carnivorous sectorial, but the tritocoue is added in 

 the form of a conical tubercle, (which is considerably smaller than 

 the protocone,) and not of a trenchant blade. In Pachycena of the 

 Wasatch and still more in the Bridger genus, Mesonyx, the gradual 

 enlargement of the tritocoue gives to the fourth premolar completely 

 the pattern of the simple tritubercular molars. 



Little is known with regard to the superior premolars of the 

 Ardocyonidce. In Clcenodon {Mlockenus) corrngatus, and presumably 

 also Aretocyon, Pa is a simple, compressed, conical tooth, supported 

 by two fangs, and therefore without deuterocone. Ij has a very 

 high and acute pyramidal protocone, on the anterior and posterior 

 edges of which the cingulum is so elevated as almost to deserve the 

 name of cusps. The tooth is implanted by three fangs and yet the 

 deuterocone is very obscurely marked. If we may provisionally 

 assign to this family the extraordinary and problematical genus, 

 Miocloenm, the systematic position of which is altogether doubtful, 

 we may mention here the curiously thick, low, rounded and 

 massive premolars, which characterize the genus. 1% has a very 

 distinct deuterocone, and in Ps this element is more or less distinctly 

 differentiated. These premolars are very much more like those of 

 some of the PerijAyehidce than they are like those of any known 

 creodont. 



/ ji J 4 >> 



Fig. 4. 

 Fourth lower premolars of the left side, internal aspect. 1, ? Tricentes subtri- 

 go7ius / 2 ? Cla:nodo7i protogonioides ; 3 Chriacus stenops ; 4 Epichriacus schlos- 

 serianus ; 5 Deltatherium fundaminis. prd- protoconid, a'^^' deuteroconidj/aj^par- 

 aconid, med metaconid. (Cope collection.) 



In the lower jaw p^ generally has a heel, formed by the more or 

 less enlarged metaconid, and thus differs from the anterior pre- 

 molars merely in its greater size and more developed heel. The 

 paraconid is rarely added, though it becomes of importance in the 

 Mesonychidce. In Dlssacns the paraconid is very small, but dis- 

 tinctly shown on p»andS which have the protoconid remarkably 

 high and acute. In Pachymna a similar condition may be observed 



