I think that the Lark name was first used on this derailleur - the 1967 Shimano Lark-W. The W designation indicates that the derailleur has no spring in the parallelogram and is controlled by two cables, pulling in opposite directions, worked by a twist-grip. Like the Shimano Archery-W and unlike later Shimano Lark-W’s, the cable nipples in this model are at the twist grip, and the clamp bolts are on the derailleur.
Aside from the W system, this is a very similar derailleur to the 1967 Shimano Skylark, except that the adjustment screws have been moved to the other side of the outer parallelogram plate - to make way for the twin cables.
This is an early example with aluminium (?) nameplate and the screw stop for the pulley cage.