UPPER CRETACEOUS MAMMALS 



97 



On quite unworn teeth a minute posterior external cingulum cusp may also be seen. 

 The internal part of the crown has one main cusp opposite and somewhat posterior to 

 the main external cusp and not over two-thirds as high as the latter. This internal cusp 

 points somewhat backward and it sends a crest forward which curves slightly exter- 

 nally and forms one side of a very deep basin — a basin, however, which is open ante- 

 riorly, save for the preceding tooth. Posterior to the centrointernal cusp is another 

 cusp, somewhat lower and on the slope of the larger one. The main internal and exter- 

 nal cusps are united by a strong and somewhat oblique transverse crest, sinking to a 

 low notch or saddle between the cusps. A less prominent ridge parallels this one pos- 

 terior to it, running externally from the posterointernal cusp. Just internal to the pos- 

 teroexternal cusp, this ridge divides, one branch skirting the external cusps posteriorly 

 and continuous with the external cingulum, the other running up the internal slope 

 of the posteroexternal cusp. The internal face of the main external cusp is furrowed, 

 several furrows passing anterointernally and one posterointernally. The external face 

 of this cusp is also marked by an irregular but distinct series of vertical furrows or 

 wrinkles. 



Two rather small circular roots support the external portion of each molar and a 

 large tapering triangular root supports the internal half. 



Skull 



Docodon apparently had a rather long and slender snout, slightly constricted 

 back of the canine. The infraorbital canal is long, opening just above the posterior root 

 of P* and anterior root of P^ The zygoma arises external to W. 



Y.P.M. 10647 I J 8 

 Y.P.M. 13769 1.7 

 Y.P.M. 13770 



Pi 



0.8 



p2 



I.O 



B. MAMMALS OF THE UPPER 

 CRETACEOUS FORMATIONS 



In North America mammals have so far been derived from three Cretaceous hori- 

 zons, the Belly River of Alberta, the Edmonton of Alberta, and the Lance of Wyo- 

 ming and its equivalents in Montana and South Dakota. Perhaps the best single speci- 

 mens are those from the Belly River, but they are very few in number and do not give 

 a good knowledge of the fauna as such. Only two very dubious single teeth have so far 

 been found in the Edmonton. The chief mammalian fauna is that of the Lance and its 

 equivalents. Some thousands of separate specimens are known, but this apparently well- 



