Hi David. That is very strange. The Mac keeps all of its disks in a folder called "/Volumes", but programs like Lightroom and the Finder are supposed to hide that unixism from the user.
I'll be honest, I have no idea. You could try renaming the disks "Photo 1", "Photo 2" etc so that Lightroom can't find them, and then try reconnecting them (right click on the item in this panel). But that is only a guess.
A