The instrument you describe is a Hawaiian Tremeloa, one of the many zany products of the Marx Musical Instreument Co. Others included the Ukelin (sometimes labelled the Guitarlin, although that may have been a knockoff built by a competitor) and the Marxophone.

The Ukelin is a bowed psaltery with chord strings under the melody strings -- the melody strings go from the bottom end to metal loops attached along the two sides, one loop per string, and were played with a short fiddle bow. The farther from the base, the longer the string and the lower the note, but the bow will contact only at most two strings, so picking out individual notes is possible.

The Marxophone had melody strings in zither fashion, but had a set of flat metal "keys," each with a weight on the end, one finger per string, which were played by pressing down on the attached end of the flat metal, causeing the weight to strike the string, hammer-dulcimer fashion. If you held the key down, the weight boing-oing-oing bounced on the string, giving you a somewhat mandolin held-note sound (technically, a tremelo).

All of these and other Marx instruments were sold door-to-door by salesmen (at a universal price of $35, if I recall), and very little decent music is possible from them. I even hate GOOD bowed psalteries. I will allow, however, that an ensemble of Marx instruments makes for a fine novelty act.

Bob Clayton