For some time I have thought it odd that people writing about Mark Twain
occasionally use the term "riverboat," although Mark Twain himself seemed
to use only "steamboat." Did he _ever_ use the word "riverboat"?

In a computer search of his texts, I found 273 instances of "steamboat" --
including "steamboating" and "steamboatman"), but not a single instance of
"riverboat" -- including open compounds, such as "river boat". (These texts
include all the books that Mark Twain published during his lifetime, most
of A. B. Paine's editions, and a few miscellaneous writings.)

I would like to hear from anyone who can document any instance of Mark
Twain's using "riverboat" in his published or unpublished writings.
(Incidentally, I didn't find the term in any of the speeches edited by
Paine, but I would be inclined to be skeptical of the accuracy of any
speech transcribed by someone else.)