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



difference in the height of the anterior and posterior 

 lobes. An nnnsnal feature is the absence of a heel in M 3 , 

 distinguishing it from the other specimens present. 



The ratios to A.mortoni Leidy (see below) show a range 

 of 45 per cent ; it is from 17 to 25 per cent more slender 

 throngh the facial part. The teeth are more nearly the 

 same size, bnt the diameters of P 3 are ont of all propor- 

 tion, being shorter and much wider. The posterior heel 

 in the older specimen of Leidy is relatively much wider. 



In many respects this small skull bears a closer resem- 

 blance to A. marslii (figs. 10-12), than to the type of A, 

 clavus clavus. 



Archceotherium sp.? 



Cat. No. 10286, Y. P. M. Probably Cedar Creek beds, Colorado. 



This specimen of uncertain taxonomic position consists 

 of the left sid,e of the skull up to and including the fourth 

 premolar, together with the rami. 



On the jaws are enormous anterior mental tubercles 

 which are triangular in section, large at the outer ends, 

 and extend widely from the rami. In this respect the 

 specimen resembles somewhat Pelonax potens, but in the 

 latter the processes extend more nearly downward. 



The teeth are like those of A. clavus darbyi in being 

 thick and in having smooth surfaces. There is another 

 resemblance between these two specimens in the rugose 

 supraorbital border of the frontals and in the wide but 

 thin dependent process from the jugal. 



P 2 is double-rooted. P 4 , a very low and thick tooth, 

 measures 30.5 X 16.2 mm. Its greatest thickness is just 

 in front of the heel, which is neither wide nor extensive. 



The first and second lower molars seem to have had no 

 heel or talonid but on the third a weak heel is shown by 

 the small lake. 



The very deep groove outside of and in front of the 

 glenoid fossa, for the reception of the point of the jugal, 

 seems to be unique in this specimen. 



Summary of Archceotherium clavus Group. 



A. clavus clavus (Marsh) : holotype, Cat. No. 12035; re- 

 ferred specimens, Cat. Nos. 10213, 10289. 



A. clavus darbyi, subsp. nov. : holotype, Cat. No. 10032; 

 referred specimen, No. 10173. 



Asp.?: Cat. No. 10286. 



