'Rounder is a flying enemy in Mega Man 5, which basically looks like a flying eye. It only appears in the first Proto Man/Dark Man stage, and it only appears near the end of that stage, before the boss. It doesn't really attack, just circles you and interferes with your shots (which could be dangerous since it appears along with the Search Mines that also appear near the end of said stage).
'Rounder 2
'Rounder 2 is a pair of larger versions of these, and they are the boss of Mr. X Stage 1. They run about on a track back and forth dropping stuff or trying to hit you.