I'm attempting to transcribe (for playback) Dukas' L'Apprenti Sorcier into Musescore.
I don't understand what the following notation means, how it should be played, or possibly be approximated, should Musescore not be able to directly play the parts as written.
I thought it might be some sort of tremolo, as the note values for the diamond notes don't fit into 9/8ths, and then there's that extra stemless A-flat above.
I was working on the score uploaded in 2007, but see that a recent, much more legible score was uploaded recently to IMSLP, so I've used that image for clarity; it appears to be faithful to the original.
Any insight will be appreciated; I don't play these instruments myself.