2 io The American Geologist. October, 1905 
lish authors). A re-study (Osborn 2 ) of the structure of the 
upper molars in the Yale Museum collection strengthens the 
tritubercular theory (Cope, Osborn) of the origin of the 
upper molar teeth. 
The Upper Cretaceous Fauna. 
Here again the relatively modernized (Osborn 3 ) ani- 
mals of the Upper Cretaceous or Laramie, although care- 
fully revised, still require elucidation from the rich collec- 
tion in the Yale University Museum. Marsh's statement 
that certain of these animals are Marsupials has been fully 
confirmed by Matthew, a fact which is striking in the ab- 
sence of any present evidence of Marsupials in the American 
basal Eocene. 
The present relations of these Laramie animals to those 
of the Basal Eocene (Puerco, Torrejon has been somewhat 
strengthened by the recognition of the ancestors (Menis- 
coessus) of Polymadodon also by the supposed recognition 
of forms related to the Amblypoda, especially to the Peri- 
ptychidre (Osborn) ; but forms certainly ancestral to the Cre- 
odonta and other Eocene mammals have not yet been rec- 
< ignized. 
The Basal Eocene Fauna. 
In this fauna, commonly known as Puerco, great pro- 
gress has been made. 
Two, sharply defined faunal stages have been distin- 
guished (Wortman), a lower, Puerco proper, and an upper, 
Torrejon (Matthew 4 ), (Compare Fig. I, 2). The latter is 
more nearly contemporaneous with the Basal Eocene 
(Cernaysien) of France. Fortunately, in Montana, a new 
localitv has been discovered for these very archaic mam- 
mals in the Fort Union beds (Douglass", Farr) which 
promises lo extend our knowledge of this fauna. 
The zoogeographical relations of this fauna, already 
established by some parallels with the Cernaysien of 
1 Ameghino, Fl . Los Diprotodontes del orden de los Plagiaulacideos. 
An. Mus. Nac, Buenos-Aires, t. ix, 1903, pp. 81-192. 
2 Palaeontological Evidence for the Original Tritubercular T/ieoty. Aiiier. 
Jour. Sci.. vol. xvii, April. W>A. pp. 321-323. 
3 Fossil Mammals of the Upper Cretaceous. Bull. Amer. Mus. Nat. 
Hist., vol. v. lv:',. pv>. 311, 330. 
4 Matthew. A Revision of the Puerco Fauna- Bull. Amer. Mus. Nat., 
PTist. vol. ix. 1897, pp. 260-261. 
5 A Cretaceous ana Lower Tertian 1 Section in South Central Montana 
Proc. Amer. Phil. Soc, vol. xli, 1902, No. 170, pp. 207-224. 
