MORRISON MAMMALS: PANTOTHERIA 67 



terior heel. The external surface is convex, the internal one excavated above the cingu- 

 lum. which runs forward from the small heel and curves into the anterior shearing 

 edge without forming an anterior accessory cusp. 



The molars, also, are of the now familiar dryolestid type, differing only in details 

 from those of Dryolestes or Laolestes. The so-called "stylodont" molar type, high, 

 slender, piercing, with confluent roots, so familiar in the literature, did not occur in 

 nature. As in all dryolestids, the pr*^ is high and sharply pointed. The me'' is slightly 

 lower, erect, tapering to a fairly sharp point, unlike that of the two preceding genera 

 when unworn. The pa"^ dififers most significantly from that of either Dryolestes or 

 Laolestes, as it is not at all procumbent. Its anterior contour is vertical. On the anterior 

 molars it is lower than the me'' in about the same proportion as the latter is lower than 

 the pr"!, but on the largest and most characteristic molars, M«-7, the paraconid is of 

 about the same height as the metaconid. Pa'' and me'' are separated by a deep, narrow, 

 V-shaped notch. The anteroposterior compression of the trigonid is progressive from 

 Ml to Me or M7 as in other dryolestids, but the trigonid basin is at least as long as in 

 any other dryolestids, contrary to the usual statement. On M3 it is about as broad as 

 long, posterior to this the breadth exceeds the length. 



The talonid, again contrary to the usual statement for "Stylacodon," is always 

 present and is at least as well developed as in Dryolestes or Laolestes. As in those 

 genera, it is triangular in plan, bearing a single cusp which is here directly posterior 

 to the me'', and narrowing as it passes outward and downward on the crown. It passes 

 into a well-marked external cingulum which runs around the base of the pr-* externally 

 and then onto the anteroexternal face, toward the tip of the pa'', which it does not quite 



reach. 



The last molar, very rarely preserved in specimens belonging to this family, is 

 here known (U.S.N.M. No. 2693). It is very small, narrower in proportion to its 

 length, and with the cusps lower and less piercing, but otherwise resembles the preced- 

 ing molars. Me is the largest tooth of the molar series. 



The molar roots are developed in exactly the same way as in Dryolestes and Lao- 

 lestes. 



Mandible 



The characters of the posterior part of the mandible are more completely dis- 

 played in U.S.N.M. No. 2693 than in any other mammalian jaw from the American 

 Mesozoic. It agrees very closely with the same parts in the English species of Amblo- 

 therium. The masseteric fossa is broad and deep. It is not distinctly bounded below, 

 nor anteriorly, where it narrows and debouches onto the external surface of the hori- 

 zontal ramus, but superiorly it is limited by a strong ridge. This ridge has its origin 

 back of and outside the last molar and it rises and passes into the anterior border of 

 the coronoid. The latter is remarkable, the apex being produced posteriorly into a 

 sharp point directed backward. This point is somewhat crushed and the possibility of 

 its being an artifact was taken into consideration but abandoned. It is quite clearly 

 original and is also seen in the English species. Between this tip and the condyle is a 



