It holds the oogermyphlip to the wotsamacallit..... Sorry Paul, Probably not a lot of help, but after half a bottle of scotch its the best I can come up with!!!!! Hopefully you will get some sensible answers
If it was a Z3 I'd say it looks like where the smog pump used to be. It's not needed here so it's been removed. Not sure if they're fitted to the Z4