Tosh,
There should be one on each side of the drive shaft tunnel. They are there for the carpeted wooden shelves to clip on to. Since your seat is backwards from every other one that I've seen pictures of (unless you have a Right Hand Drive car), I would assume your seat was "home made" by someone.
Does your third seat have a back rest?
If yes, where is the chrome handle that opens the soft top boot?
If no, doesn't the passenger hate getting the soft top boot handle stuck in their back?
Does your data card indicate the third seat?
Thanks,
Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both tops
1994 E420