114 AMERICAN MESOZOIC MAMMALIA 



Cimolomys primaevus (Lambe 1902) 

 1902. Ptilodus frimaevus, Lambe, Contrib. Canad. Pal., XXX, 79. 



Type. — Geol. Surv. Canada. Right lower jaw with P4 and Mi. Fig'd, Lambe 

 1902, PI. XV, figs. 13-14. 



Horizon and Locality. — Belly River beds. Alberta, Canada. 



Diagnosis. — P4 with eleven serrations. Mi formula 6:4. Specific or generic char- 

 acters inadequately known. 



This specimen is important as the only known multituberculate from this horizon. 

 The original has not been studied by the present writer, but Lambe's description and 

 figures are clear. The dental characters are given as follows: "Fourth premolar with 

 eleven serrations on its edge; on its inner side, five complete grooves preceded by a half 

 groove. First molar with four tubercles on its inner side and six tubercles on its outer 

 side. . . . There is a slightly backward curve of the tubercles on the outer side of the 

 first molar. ..." Matthew (1916) stated that Lambe's type is "certainly related to 

 Cimolomys of the Lance and apparently not generically separable." From what is now 

 known, even the species cannot be proven to be distinct from that of some of the Lance 

 specimens. It is so improbable that a species, or even a genus, of mammals is really 

 common to these two very distinct faunas, however, that further material would almost 

 surely serve to separate C. -primaevus from any Lance form. 



Essonodon Simpson 1927 

 1927. Essonodon, Simpson, Amer. Mus. Novitates, No. 267, 2. 



Definition. — M2 broader than long, cusp formula 3:2, two external roots, and 

 one internal. 



Type. — E. browni Simpson. 

 Distribution. — Hell Creek beds, Montana. 



This genus is very poorly known but it is quite noteworthy from a morphological 

 point of view in the extreme anteroposterior compression of Mo and its small cusp 

 number. 



'Essonodon browni Simpson 1927 

 1927. E. browni, Simpson, Amer. Mus. Novitates, No. 267, 2. 



Type. — Amer. Mus. No. 14410. Isolated M2. Fig'd, Simpson 1927, fig. i. 

 Horizon and Locality. — Hell Creek beds. Crooked Creek, Montana. 

 Diagnosis. — Sole known species of the genus. M2 2.4 mm. long, 3.6 mm. wide. 



Order MARSUPIALIA Illiger 18 11 



Definition. — Primitive cheek tooth formula P| M* . Typically with replacement 

 confined to last premolar. Angular process of lower jaw inflected (save in Tarsipes). 

 Typically with nasals expanded posteriorly, jugal taking part in glenoid fossa, and 



