hippopotomonstrosesquipedalian

JM has been invited to address the Hippopotomonstrosesquipedalian Appreciation Society and, in a word, accepted!

I saw another misspelling of hippopotomonstrosesquipedalian go scrolling by on the Wordie home page, and began wondering who coined the term. It's sometimes said to be from Mrs. Byrne's Dictionary (1974), but I've found it in The American Thesaurus of Slang (2nd ed., Berrey and van den Bark, 1953).

From the hippopotamine root, it looks like it should be spelled "hippopotamonstrosesquipedalian" or "hippopotamomonstrosesquipedalian" as Richard Lederer did in Word Wizard (2006). I'm curious if the original coiner really did form it as "hippopot-o-monstr-o-sesquipedalian".

A very long word (really, that's what it means).