My dear bro :
a letter from Samuel Clemens to his brother Orion.
APA Citation
Twain, M., Grolier Club. (1961). My dear bro: a letter from Samuel Clemens to his brother Orion. [Berkeley]: The Berkeley Albion.
MLA Citation
Twain, Mark, 1835-1910, and Grolier Club. My Dear Bro: a Letter From Samuel Clemens to His Brother Orion. [Berkeley]: The Berkeley Albion, 1961.
Warning: These citations may not always be complete (especially for serials).