The object of this bulletin is twofold: To call attention to the richness of the United States National Museum North American land mammals, and to furnish a summary of the systematic results of the study in this field to the end of the year 1911. North America is understood as the entire continent from Panama northward, together with Greenland and the Greater and Lesser Antilles. In no other museum is the mammal fauna of so large an area so fully represented.