How tall and how long is the breeder? O. hummelincki and A. aculeatus are likely reasonable choices IMO IF you have a sump. 40 gallons is pushing a water quality issue without a sump and height is a concern for keeping a skimmer octoproofed in a shallow tank (normal recommendation is to drop your water line and inch or more below normal (ie 2-3 inches below the top). With a sump, the extra length of a breeder should compensate for the smaller than recommended 50 + gallon tank. If a nocturnal suits you, the small macropus that is sometimes offered from Live Aquaria (I believe they have one now, or did yesterday - see octo availability for a link) would also work. I particularly like this species and have kept both a male and a female but they are VERY nocturnal.
Alright thanks I beleive the tank was 36 x 18 x 16 or 36 x 16 x 16 i believe it was the first one though. And sorry to say but I can't pull a sump off in the tank cause the stand its on and I can't move it either... So I think octo's are out of the question then. Would a cuttle fish fair off better or would it be worse?