Dear Mr. Kelly,
Though I am no Twain scholar, the idea of pornography as your student (I
think) intends it is an entirely 20th century creation. Erotica, which
flourished in Clemens' time and before, is something else again. The best bet
may be to find MT's railings aginst hypocrisy, with which his later nonfiction
work is full.
Kathy O'Connell