I recently saw Black Sabbath doc which said (I think it's well known) that whilst Iommi wrote most of the riffs for Sabbath, Geezer Butler wrote the majority of the words.
I think that bassist Bob Daisley wrote the lyrics for the Ozzy albums he was on too.
So are there any other notable cases where the bassist (or drummer, guitartist) etc. writes the lyrics for a band, but they are not the singer or the music writer?
( so not Phil Lynott - he was the singer, not Nikki Sixx - he wrote the tumes too)
A couple of non-bassists spring to mind........