436 E. ~L. Troxell — Entelodonts in Marsh Collection. 



the anterior notch so uniformly found in the family. The 

 tooth is wider than long (34 X 31 mm.) ; is completely en- 

 circled with a cingular ridge (except a short space on the 

 outer side) which posteriorly is heavy, and it has a sharp 

 longitudinal valley deeper on the rear side. The straight 

 anterior side of this tooth resembles that of the much 

 smaller Entelodon magnus of Europe. 



The first molar is irregularly squared, the anterior side 

 is rounded, the exterior bilobed. Postero-internally, the 

 sides combine in a smooth curve except that at the root 

 there is a sharp corner. The inner side is vertical and 

 the tooth is not wider at the roots as in M. latidens (fig. 

 17). The cingula are strong and especially notable ex- 

 teriorly and interiorly between the lobes. 



The second molar, subquadrate, is a little wider in front 

 and on the outer side; postero-internally the corner is 

 rounded. The cusps are widely separated and the proto- 

 and metaconule and also a metastyle and a mesostyle can 

 be seen. Though the outer cusp seems to arise from the 

 cingulum, it is still the hypocone, and shows the source of 

 its development. (See cusp indication, figs. 17, 18.) The 

 internal cusps, especially when slightly worn, form lophs 

 and resemble those of some perissodactyls. This tooth, 

 a little larger than M 1 , has a length of 40 mm. and a width 

 of 42.5 mm. anteriorly. 



The third molar is roughly triangular, having all the 

 corners rounded off. The sides are straight on the front 

 and outer faces and form an acute angle because of the 

 prominence of the base of the paracone. The cingulum is 

 strong anteriorly, but there is none externally. The pro- 

 tocone is slightly in front of the mid-line ; the protoconule 

 is scarcely more than a small ridge ; the hypocone is weak 

 but stronger than the cingular cusps; the metacone is 

 small and worn and the heel is very indefinite. 



Of this specimen, the skull only is known, which is well 

 preserved up to the alveoli of the canines. 



Summary of Megachoerus zygomaticus Group. 



This specimen Peterson referred to the genus Pelonax; 

 it is here made the type of a new genus and species, Mega- 

 clioerus zygomaticus, and the important characters which 

 distinguish it from all other American genera are : the 

 small P 1 separated from P 2 by a long diastema, the less 



