If the cars are all the same, and I suspect that they are, there are two bolts in the back as well. One for each seat rail. It is easier to access if the seat is moved as far forward as possible.
I don't think the seat can be removed without removing these bolts. My recollection is that the bolts go through the seat rails and the wooden wedges under the rails, and are bolted right through the floor boards.
Cheers,
