The Elise uses 2 ducts on the underside which I assume are there to take cold air into the engine bay. The photo shows the 2 trays removed for servicing, the larger one is at the front of the engine bay, the smaller one at the rear valance. Once in place it's going to be a very neat air flow underneath.
Cold air for the engine comes in via the LHS side vent with trunking that leads from the vent directly to the airbox. (which is a PITA to replace with the rear clam on)
Brian