The Bosporatai in the Cherosones get their name from the Cimmerian Bosporus (todays straits of Kerch). AFAIK the spelling of either is fairly interchangable so you'll see them both refered to as either Bosphorus or Bosporus. I usually use Bosphorus for the southern region and Bosporus for the the northern (mainly because I've always seen the greek kingdom in the crimea refered to as the Bosporan Kingdom).