sparky, this is the doohickey I was referring to, a pretty neat system to cover the chain so that in really bad conditions, you'd have less mud and such getting all over the chain and rings, kinda neat, but I suspect it is rather exclusive, and probably expensive. I read this cgoab trip journal a few years ago and remembered this thing. Worked for them in any case, journal is Panamericanos on the pan american or thereabouts.
makes sense to me to cover it all up if there is no derailleur, as mentioned though, its probably pretty rare.