The Hohner Primatona IV button accordion.

The following is from an early 1960's Hohner ad: "A two row model in an entirely new design, specially built for
Ceili Music. Mussette tuning, finished in red or black. 21 treble keys and 8 bass keys, 4 sets of finest steel reeds,
3 treble finger tip couplers. Tuned in B/C, C/C# or D/D#". Cost is 33 pounds, about $100 at that time; same as Paolo
Soprani.

The one shown below is tuned B/C and is black.