It's just soldered RAM with a single SO-DIMM slot above it. Nothing particularly special except it shouldn't be there.

It occurred to me after posting that it could be a third-party card, but the processor+RAM board says Apple Computer. It's similar to the layout of the Crescendo/WS, with only one slot there as well ( http://www.sonnettech.com/product/crescendo_ws.html ).

Edit: and just to be even more mysterious, the manual (which it came with) says there is also only one RAM slot.