[R] Add dots at the mean of a bwplot using panel.points

[Andy Bunn]

How can I modify the example below to put a dot at the mean of each violin
plot? I assume I use panel.points but that's as far as I can go.

     bwplot(voice.part ~ height, singer,
            panel = function(..., box.ratio) {
                panel.violin(..., col = "transparent",
                             varwidth = FALSE, box.ratio = box.ratio)
                #panel.points(mean(x.....))
            } )

TIA, Andy