Bike porn

isn't a mixte the type of step-through that has a pair of stay-sized tubes instead of a top tube, which run all the way from the head tube past the seat tube down between the seatstays and chainstays?

Yes.

Which makes me wonder, is there a name for the half marathon step through which has a single tube from headtube to seat tube supported by a pair of stays from that junction to the dropouts?