No, that's not it. I'm looking for a rear valance. The mock up car in the Ulster Folk & Transport museum has this piece, as does at least one of the pre-production cars that was used as a mock-up for the AmEx gold car brochure.
It is even depicted on the early brochures where instead of seeing the muffler, crank case, and most of the rear suspension, all that is visible are the fins on the bottom of the oil pan.
Lotus always installed one of these pieces on the Esprit:
I would love to see one of these, and how it was mounted in order to create one for my own car. I have read that if not properly reinstalled on an Esprit it can adversely affect fuel economy. I've no idea how true that is, but it would at least look a whole lot nicer to clean up the rear of the engine. Tow hooks might be a problem, but I'd figure that one out later.