Claudius

A month invented by the Noreascon II treasury staff to make bookkeeping easier. It lies between August and September and covered the traditional Worldcon Labor Day dates. Treasury closed the books for August, opened the books for Claudius during which Worldcon ran and then closed them at the end of the con, subsequently opening September's books.

Noreascon II was audited by the IRS which thought the extra month to be amusing, but harmless. (That's pretty much what they thought of Noreascon's account books, also.)