'Rounder (ラウンダー) is a flying enemy in Mega Man 5, which basically looks like a flying eye. They travel in a pair and only appear in the first Proto Man/Dark Man stage at the end of that stage, before the boss. It doesn't really attack, just circles around Mega Man and interferes with his shots (which could be dangerous since it appears along with the Search Mines that also appear near the end of said stage).
'Rounder 2 is a pair of larger versions of the 'Rounder. They are the boss for the first Mr. X's stages, at the top of what seems to be the outer wall. They run back and forth on a track while dropping bombs and trying to hit Mega Man. They're vulnerable to the Flame Blast and a charged attack from the Power Adapter, which is able to change their direction.