A standard Magistroni 3-arm crankset. "Senior" cranks are 3-arm, 116mm bcd, with cutouts in each arm, stamped "L. Magistroni Senior" (see below) on the crankarm face in between 2 short flutes.
Above is seen what appears to be a "Senior" crankset, but with "Made in Italy" rather than "Senior" stamped below "L. Magistroni".
Another set of "Senior"-like cranks, with "Magistroni" inside an oval rather than the usual stamping.
An example of what look like "Senior" crankarms, but without the "L. Magistroni Senior" stamping, and with "Bianchi" script instead.