The Shimano Lark is a Skylark with the cable clamp bolt mounted on a sprung ‘cable saver’ arm. I have always liked this feature as it gives a pleasant supple feel to the gear change.
I think this example is the first version with the aluminium(?) nameplate and screw pulley cage stop.
I have catalogued this derailleur as being ‘gold’, but I suspect that the name plate would, at one time, have had a painted background. However, only Grissom from CSI could tell us if this is true by analysing microscopic traces of tell-tale blah blah blah etc. etc. etc.. In the mean time we can appreciate it as a possible piece of 1960s bling - a suitable subject for a wager between Sir Bernard Docker and Auric Goldfinger.