Jun 29, 2012
New Symbol MIDU (from MWJ) reflects a new underlying index. The S&P Mid Cap 400 index is technically the new stated index (previous was the Russell Mid Cap Index). Of course, as a leveraged product -- MIDU doesn't actually track either of those, it attempts to track a daily leveraged return of the index.
http://www.direxionshares.com/pdfs/SP_PR_060712.pdf