I'm researching a different Wm. Mewes, also from Prussia. Mine lived in IL & MO and died in MO. Don't know if you know about the death certificates online at http://www.sos.mo.gov/archives/resources/birthdeath/
but I know I've seen the name Pendleton on one or more of the certificates I was sorting through. I think Mewes was eventually changed to Mavis because that's how it was pronounced in German (not like a cat's mew) and the only way to get English speakers to pronounce it right was to change the spelling so they could figure it out.