Ten envelopes. One is marked First Day Issue. Cachet envelopes representing various U.S. figures, and states. Each envelope was designed to be issued with a specific stamp or stamps.
 
Maj. Powell's Exploration of the Colorado River,
100th Anniversary of the Exploration of the Colorado River,
John Sloan; American Painter,
William M. Arnett; American Artist,
Missouri Statehood,
Eisenhower Memorial,
White House Flag,
South Carolina 300th Anniversary,
2 Mississippi Statehood.
These were samples of proposed envelopes for the specific series the US Post Office was working on. I have not been able to find others like them. Rare envelopes now to find. Not in MINT condition but, very good and would be wonderful to send out a nice old fashion letter.