How can I stop Calibre running at startup?

I have Calibre installed on a netbook running Ubuntu 12.04. It was doing fine till a few days ago when it began running at startup. Because the Calibre library is on a partition which does not auto-mount at startup, Calibre then complains that it cannot be found, and offers to create a new library. It was precisely to avoid this situation that I'd not added Calibre to Startup Applications. I checked my startup applications list again. Calibre isn't on it, & yet runs when I start my netbook. How can I stop it doing that?

Thanks in advance for any help.