Missing parts?

I noticed a slight fuel leak on my '76 300D this afternoon. It's quite small so it didn't bother me at first, but then I noticed that there was a hose hanging there as well. On top of the fuel filter there is an apparatus that I think is the shut off , kinda saucer shaped and when it's running the center pops out and when I shut it off it goes back inside the "diaphram" for lack of a better word. I think there is supposed to be some kind of nipple or something that goes on there and this hose is supposed to plug into it, does anyone have a pic. of a 115 chassis engine compartment so I can compare or can someone figure out my inadequate discription of what I'm trying to describe? TIA Tom