Am. Jour. Sci., Vol. XLVI, 1893. 



Plate XI. 



Quartern. 



Phoi 



Mia 



Loup Fork 

 John Day 

 }YhiteRhei 



Bridger 

 Eo Cerie Wahsatch 

 Pixerco 



Crelcxceoxis 



Ji 



itrocssic 



Z^arami: 



Allantos, 

 -rus 



Alonotrema 



77" 



riassie 



ermian 



fromammalia T hero morphia. 



*J)ai i ro-Alam m alt 



Hypothetical Phytogeny of the Xorth American Mammalia. 

 The Monotremcs disappear in the basal Eocene. The Marsupials disappear in 

 the upper Cretaceous and reappear in the lower Miocene, (Didelphys). The ab- 

 errant Placentals branch off in the upper Jurassic. The typical Flacentals divide 

 into the ,: Ancient types " dying out in the Miocene, and the " Modern types " 

 still existing. The aberrant Placentals are given off in mid-Mesozoic times. 



