Thanks 'Spaw, even a musical klutz like me understood your explanation. I assume you don't have to stuff your fist up a mellophone (carefully avoiding potential jokes!). Certainly the mellophones in the Fate Marable pictures in my reference books look the same shape as french horns, unlike the modern Kenton one which is shaped like the marching band one in the link RichM supplied.
I always thought trombones in a marching band added to the potential for disaster.
Perhaps we ought to revive the NYCFTTS Marching and Drooling Band?
RtS