Columbia subject headings:
Authors, American--19th century--Correspondence.
Twain, Mark, 1835-1910--Correspondence.
Harvard subject headings:
Authors, American--19th century--Correspondence
Twain, Mark, 1835-1910. Correspondence.
Princeton subject headings:
Authors, American--19th century--Correspondence.
Twain, Mark, 1835-1910. Correspondence.