The first cello banjo (also sometimes referred to as a bass banjo) was a 5-string (gut) instrument with a 3" deep 16" diameter rim, marketed in 1889.
In 1919, Gibson began manufacturing a 4-string cello banjo, and a separate 4-string instrument called a bass banjo from 1930-1933 which was played as an upright bass.
Gold Tone is the only contemporary manufacturer, with a cello or bass banjo having a 32" scale and a 13" pot.