MORRISON MAMMALS: PANTOTHERIA 63 



becoming obsolete beneath the pH-mc^' notch in passing externally, it continues, becom- 

 ing narrower and lower on the crown, and passes into a low and rounded horizontal 

 external cingulum on the base of the pr"*. On the middle cheek teeth the pa"* and talonid 

 cusp are not in line with the mc^, as in Dryolestes, but are somewhat internal to it and 

 are connected across its base by a nearly horizontal swelling. This character is first 

 definitely indicated on M3, reaches a maximum on Mo or M7, and is slightly less again 

 on Ms. On all the molars, except as modified by wear, the me"* is very slightly lower 

 than the pr"*. 



Mandible 



The mandible is very like that of Dryolestes, and its general characters vary but 

 little within the family. In dealing with dryolestid lower jaws the marked differences 

 between the internal and external aspects have often proven to be a stumbling block. 

 These differences are very clearly brought out in the present material. The internal 

 surface is flattened and the mouths of the alveoli are here higher than externally. The 

 external aspect is rounded, with the mouths of the alveoli lower. Thus when only the 

 inner side is visible one apparently has a very stout jaw with low molars implanted 

 by two roots, while in external aspect there is apparently a slender jaw with high 

 molars implanted by only one root. 



The coronoid is somewhat confusing in the published figures of the type jaw (e.g., 

 Marsh 1887, PI. IX, fig. 2) as it is here much broken. Actually it arose immediately 

 back of Mg, was high, broad, and somewhat recurved. The condyle is somewhat above 

 the alveolar level, as in all pantotheres, and has an articular surface of irregular oval 

 shape. 



The angle is of dryolestid type, small, styliform, not at all compressed trans- 

 versely, separated from the condyle by a large semicircular notch. The pterygoid fossa 

 is bounded below by a low sharp pterygoid crest, and has the dental foramen at its 

 anterior end, but little posterior to the last molar. On Y.P.M. No. 10662 there is a 

 mental foramen beneath the posterior root of Pi. This specimen also has the internal 

 groove discontinuous, interrupted beneath M* — an individual variation. 



Measurements 



Lengths : 



Pi Po P3 P4 Ml Mo M3 M4 Ms Me Mt M 



8 



Y.P.M. 13719 0.7 0.8 0.8 .. I.I I.I 1.2 1.2 1.3 1.3 1.2 1.2 



Y.P.M. 10662 1.4 i-i 1-2 1-3 1-3 



U.S.N. M. 2727 .. i.o I.I I.I I.I 1-4 



Y.P.M. 13720 1-2 1-4 1-4 1-4 1-3 



Y.P.M. 137 19: Depth of ramus below Mg, inside 4.0 



Length Pj-M, i3-3 



Anterior end to tip of angle ca. 28.0 



, , ,, (inside 3.8 



Y.P.M. 10662 : Depth of ramus below M< |mjjj.jjg ^.o 



