>Medieval legend?
The medieval legend refers to "Magor", i.e. "Hunor" and
"Magor". But these probably reflect the dual ethnic-linguistic
situation within the Hungarian confederation: the Turkic (Onogur)
ruling strata, and the ugric Magyars.
Meshcherskaya nizmennost, Meshcherskoye, in Russia, contain an
older version of this ethnonym.
http://www.maplandia.com/russia/penzenskaya-oblast/serdobskiy-rayon/meshcherskoye/
(I don't know whether there is or there is no link to the name
of another Ob-Ugric people, the Mansi people (living in the
Khanty-Mansi autonomous region).
George