http://www.themodernantiquarian.com/post/33695

Looking at this picture the CnRs seem to have what I would call 'an inverted gutter'. Almost like a little raised causeway across the rings.

I've seen gutters often enough, but have never really noticed this kind of feature before. How common is this?

I suppose it just makes the rings penanular (or whatever the word is), but with the gap being so slender it does look more like a causeway type thingamy whatsit. The penanular rings I've seen have had a larger break in them than this.