Thanks to all. Probable next steps: take the broken ring off, insert and glue the fragment into place, reattach when glue fully cured. [Possible obstacle: I see now that the ring is slightly bent, lifting off the housing about 0.5 mm at one end of break.] Search for parts-only replacement. Learn what repair shops suggest.

Asides: Thanks, Nick. I have heard of "city", but not seen one around here. We are neck and neck with Wyoming, both near 600K total, about as many as Portland OR. David, yes, yes and yes. Had not considered a hood for this lens.