Magno-tone resonator guitars were made by Dobro and included the Cyclops and double Cyclops guitar (with a single central screenhole was or two smaller ones in a single frame respectively). Dobro typically used the Magno-Tone, for the instruments sold through Montgomery Ward. The single Cyclops were made from around 1932 to 1933 and were then replaced by the double-Cyclops guitars made from 1933 to 1936.  Some Magno-tones were made by Regal.

Source: The Hawaiian Steel Guitar and Its Great Hawaiian Musicians. Lorene Ruymar. Centerstream Publications, 1996

Source: Vintage Dobros: A Guide. Tom Gray. Vintage Guitar Magazine. June 1999.