“Lantern gears” is a term, apparently originating from Matthias Wandel, for a kind of gear that was ubiquitous in medieval clocks: two parallel discs joined by a circle of round bars around their perimeters. It would be a lantern if you put a candle in the middle. If it weren’t for the discovery of the Hellenistic-era triangular-tooth-profile Antikythera Mechanism, I would have thought they predated meshing spur gears.
While it’s tricky to get involute-profile gears to mesh without binding if they have fewer than seven teeth, lantern gears can work well with as few as three teeth, because the mating gear’s teeth can sweep around the interior of the lantern gear. Medieval clocks, with their more primitive toothforms, did not come close to this level of optimization, but I think they did get substantially better gear ratios than they could have managed with triangular teeth.