E. L. Troxell — Entelodonts in Marsh Collection. 445 



convex. Behind the tubercles the body of the ramus is 

 unusually narrow, 60 mm. 



The right posterior mental tubercle is hardly more than 

 20 mm. long. That on the left side (now broken off) was 

 much smaller; but one is led to suppose that the rough- 

 ened area on the ventral border of the ramus, just an- 

 terior, served in its stead for the attachment of the buc- 

 cinator muscle, as in the carnivores to-day. 



The canines in the rami, like those in the upper jaw, 

 are long, slender, and recurved. They curve back so far 

 that the points actually come in contact with the upper 

 canines and therefore wear to sharp edges like those of 

 rodents. P x is small and two-rooted and, as previously 

 stated, is situated near the canine and P 2 . The other pre- 

 molars join practically without space. P 3 stands high 

 and its shelf-heel is apparently wide. P 4 has a very 

 broad heel with numerous tubercles on it. Its breadth is 

 27.5 mm. and its estimated length not more than 36 mm. 



Mj, though worn, shows the general proportions of 

 ArchcEotherium ; its diameters measure 31 by 26 mm. M 2 , 

 36 X 30 mm., is wide across the proto- and metaconids 

 which are strong, and there is a definite heel. M 3 is 

 much like M 2 but slightly narrower. On all these molars 

 the cingula are weak, except the anterior one and that 

 around the base of the hypocone. On each the posterior 

 heel is fairly strong. 



Summary of Choerodon caninus Group. 



The genoholotype is found in the Middle John Day beds 

 of Oregon. It resembles Archceotherium in many gener- 

 alities, but differs in the long curved canines and depend- 

 ent processes from the jugal, in the greater size, and in 

 its wide geographical and geological separation. It re- 

 sembles the genoholotype of Megachcerus zygomaticus in 

 the greatly enlarged dependent processes, but it is one 

 fifth smaller, does not have the pitted teeth, has a notch 

 anteriorly in P 4 , and very short diastemata. It differs 

 from M. latidens in having narrower lower molars, espe- 

 cially behind, high anterior cusps and the much smaller 

 size. It has about the same size, age, and location as 

 Choerodon calhinsi, but is separated specifically in having 

 the larger canines and longer, more recurved dependent 

 processes, and by the presence of strong tubercles on the 

 chin. 



