Addressees: Twichell, Harmony C
- Samuel L. Clemens to Joseph H. and Harmony C. Twichell, 18 November 1868 · Cleveland, Ohio · UCCL02765
- OLC to Joseph H. and Harmony C. Twichell, 31 October 1869 · Elmira, N. Y · UCCL00369
- Samuel L. Clemens to Joseph H. and Harmony C. Twichell, 12 November 1870 · Buffalo, N.Y · UCCL00533
- Samuel L. Clemens to Joseph H. and Harmony C. Twichell, 19–22 March 1872 · Elmira, N.Y · UCCL00735
- Samuel L. Clemens to Joseph H. and Harmony C. Twichell, 11 June 1874 · Elmira, N.Y · UCCL01097
- SLC to Joseph H. Twichell and Harmony C. Twichell, 24 December 1885 · Hartford, Conn · UCCL03342
- Clara L. Clemens to Harmony C. Twichell, 1 October 1909 · Redding, Conn · UCCL10632
- SLC to Joseph H. Twichell and Harmony C. Twichell, 27 December 1909 · Redding, Conn · UCCL08525
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