E. L. Troxell — Entelodonts in Marsh Collection. 373 



Specific characters of A. clavus clavus. — The smallest 

 of the entelodonts, distinguished from A. mortoni by the 

 wide heel, the narrow crown, and the flat, outer side of P 3 , 

 by the great antero-posterior extent of P 4 , and by the ex- 

 treme slenderness of the face (70 to 79 per cent) in front 

 of the orbits. 



This sub-species may be generally known by the slender 

 processes and general structure of the zygomatic arch, the 

 lack of foramina on the anterior wall of the temporal, the 

 jugal forming no part of the glenoid cavity, the smooth- 

 ness of the f rontals above the orbits, the wide lachrymal, 



Fig. 9. — Archceotherium crassum (Marsh). Holotype. Cat. No. 12020. 

 Side view of zygomatic arch and dependent process. Compare Fig. 10. 

 One-fifth nat. size. 



the large double-rooted premolars (especially P 2 ), the 

 first premolar set at an angle in the maxillary, the long 

 slender canines, the sub-quadrate P 4 having equal dimen- 

 sions, the straight-sided M 2 , narrower behind, the sub- 

 triangular M 3 , and the strong heels on all the teeth. 



The associated specimens are Nos. 10213 and 10289, 

 both young individuals which correspond closely in the 

 size of the permanent teeth and in the small anterior men- 

 tal tubercles, as yet probably undeveloped. 



A. clavus darbyi, subsp. nov. — An allied type of entelo- 

 dont, constituting a subgroup, is represented by the speci- 

 men No. 10032, and with it another, No. 10173. It seems 

 to approach more closely A. mortoni than A. clavus clavus 

 does, but it is distinguished from that species by the 

 greater transverse diameter of P 3 , 119 per cent, con- 

 trasted with its short antero-posterior diameter, 87 per 

 cent. 



