Conn 4M Curved Soprano
Date: 1937. Owner unknown
Conn produced soprano saxophones through 1941, or serial number 300xxx. The 4M may have been available between 1941 and 1969 on special order, based on "New Wonder" tooling (source: Saxpics). The question is whether there was a "standard" series soprano at all, different from the New Wonder II model. It is suggested by various sources that the series after the New Wonder II was built ¾" longer, requiring a different, shorter, mouthpiece.
From what I have been able to infer from various sources on the internet, including this review by Thomas Zinnen of an 18M New Wonder II straight soprano, the sound of Conn's soprano saxophones was "awesome", however at the price of being finicky with mouthpieces. The "trick" appears to be in either the size of the chamber of the mouthpiece (larger during that era than in modern mouthpiece) and/or the length of the instrument being longer, thereby requiring a shorter mouthpiece. Apparently around 1929 Conn lengthened their soprano saxophones, thereby requiring a short soprano saxophone mouthpiece. This means that the 4M will probably only work properly with period Conn "short" soprano saxophone mouthpieces. Anything else is out of tune.