E. L. Troxell — Entelodonts in Marsh Collection. 367 



In M 2 , the metaconid, as is the usual case, has a double 

 point on the cusp. This may really be the meta- and 

 paraconids closely combined (see cusp indications, fig. 

 18). Both are found in some earlier forms such as the 

 artiodactyl Trigonolestes. Taking into consideration 

 that in Archceotherium the posterior cusps are never as 

 high as those anterior, the hypoconid is strongly devel- 

 oped; on the other hand, the entoconid is weak. A dis- 

 tinct posterior heel may be seen. M 3 is much like M 2 ex- 

 cept that a very marked posterior heel and a less strong 

 hypoconid are observed. The posterior half of the tooth 

 seems to be rotated inward, throwing its vertical axis out 

 of parallel with the first half. 



Fig. 4. — Archceotherium clavus darbyi, subsp. nov. Holotype. Cat. No. 

 10032. Side view of skull and jaws. One-fifth nat. size. 



Archceotherium clavus darbyi, subsp. nov. 



Holotype, Cat. No. 10032, Y. P. M. Oreodon beds (Middle Oligocene), 

 Harrison, Nebraska. 



This specimen (figs. 4-8) consists of a nearly complete 

 skull, the posterior portion of which is almost perfect. 

 The tips of the dependent processes are lacking, also the 

 right premaxillary and the body of the ramus. The speci- 

 men was found by Mr. Fred Darby on the Peabody 

 Museum Expedition of 1914, in the Oreodon beds near 

 Harrison, Nebraska. 



The zygomatic arch at once strikes one with its inter- 

 esting and perhaps unique features. The structure is 

 moderately heavy in comparison and the dependent pro- 

 cess in its narrowest part is 48 mm., or 14 mm. broader 

 than that of A. clavus; the depression immediately be- 



