Gibson 7 String, Unusual Model

I was visiting Carter’s Vintage Guitars in Nashville, TN and I saw this unusual 7 string Gibson resonator guitar. Unfortunately I didn’t get to play it. I would love to hear how it sounds. Oh well, maybe it will still be there the next time I go to Carter’s. If you know more about this model of Gibson guitar, please send me a message. I would like to learn more about it.