But I'm still baffled by what I thought was an image of the inner edge, the uppermost section of the bright band across the middle of the planet.

I think that's a combination of the rings, and the ring-light illuminating the surface of the planet itself. The relatively sharp dark line across the equator is there because the rings block most of the light reflected off them when seen edge on, so the clouds along the equator get less ring-light.