διὰ νήσων τὸν πλόον ἐποιεῦντο → they kept sailing through the islands
commistim ADV :: jointly, in a mixed manner
commistim: (commixtim), adv. commisceo,I in a mixed manner, jointly; opp. separatim, Hier. praef. in Isa.
commistim, -io, -ūra, s. commixt...