I believe it is a chain guard to prevent the chain from dropping off the small ring on high low shifts and getting lodged between the bottom bracket and chain ring. It looks to be stationary (not moving with the mech).
Seth Romanow
Bellevue, WA USA
> On E-Bay there is a gorgeous NIB Super Record group modified by the Swiss
> Firm ICS. Item # 150247904311.
>
> The front derailleur has a feature I am unfamiliar with. It is a white
> plastic guide of some sort that seems to protrude forward and downward.
> Perhaps one of our more mechanically knowledgeable members could reveal
> it's
> purpose and tell us if it was effective or whatever. Very interesting
> looking thing.
>
> Tom Sanders
>
> Lansing, Mi USA