Melodeons et al

Melodeons are bottom accordions traditionally used in folk music. From time to time we find older instruments in town, including many of these accordions and perhaps one of the oddest is the unamed diatonic melodeon shown above with a strange bass key work.... Has anybody seen something like this before?

Thierry Beuzer makes and restores in France bottom diatonic accordions or melodeons. One of the Hohner marine series he sells is the so called three row Valparaiso model in G/C/.