Plastic part under radiator...what is it?

[TWOZTER]

Changed the cooling system (Rad, WP, thermo...etc.) and left the plastic shield off to check for leaks....but like an idiot left the plastic piece that was hanging below the radiator....then promptly drove over it as it fell off about 3 miles down the road. Dealer can't seem to find it on the system or at realoem. Any of you fellow 1998 MZ3 buds know what this dang part is? It wasn't very big (maybe 18 inches long?), and seemed to hook onto a lip either on or right below the radiator. Air duct? Splitter? Tried searching here and couldn't find a definite answer....

[ZGator]

Part # 51718397359

Air Dam or Underbody Shield

http://www.rmeuropean.com/Part-Number/Undercar-Shield-Center-Front-__51718397359_GEN_E095124A.aspx

Did something similar myself - bought a new one, put it on, then promptly put a hole in the new one when I hit a cone at cca event - I think.. Other z3 forum there is talk of getting a more rugged one, like aluminum..

I am not sure if it is there for protection, or air flow - or both, personally I am about to remove both my plastic shroud and this thing.

[TWOZTER]

...or at least the pieces of it. Luckily, one of the pieces had the part number on it. If anyone is interested, its #51712496714 "Air Duct, bottom, front" according to BMW. $45.