34 Bulletin American Museum of Natural History. [Vol. XIV, 



ossifraga, rectangular in outline when seen from above with high 

 stout protoconid ridged before and behind, large well separated 

 trenchant heel, and smaller less trenchant paraconid. The pro- 

 toconid is vertical in m-g-, projects slightly forward in m-j, and 

 somewhat more backward in my. The second molar is the 

 largest and the third the smallest of the three. 



The angle of the lower jaw is inflected, more so than in Dis- 

 sacus or P. ossifraga, less than in Mesonyx uintensis. In M. 

 obtusidens'''' \ht angle is prolonged into a stout hook much like 

 that of Stypolophus " (Scott, '87, p. 157), hence is quite different 

 from the other Mesonychidae, in which there is a progressively 

 increased inflection of the angle, reaching a maximum in the 

 Upper Eocene Mesonyx uintensis where it is almost like that of a 

 Marsupial. 



Fig. 15. _Pachycenagigatitea^'iio.2^^<). Left femur 

 and right tibia, from in front, one-fourth natural size. 



Fig. 16. Pachycena gi- 

 gantea^ No. 2959. Right 

 ulna and radius, one- 

 fourth natural size. 



The skeleton is very massively proportioned ; the limb bones 

 are somewhat shorter than those of P. ossifraga, but one- 

 fourth thicker in the shaft, although the animal is not full 

 grown. The few dorsal vertebrae preserved are short and thick 



