The bolon is a hunter's harp from lower Mali. There is an interesting progrssion that took place in the string instrument development.
According to the hunter's and griot's I spoke with over 9 years in Mali the bolon is the original hunter's harp and was once used to play for the most honored of people. It is still used to play at funerals of very important people.
The bolon may have morphed into the 6 string doson n'goni (2 sides of 3 strings each, pentatonic scale), and the 7-string simbi (inline strings, minor scale).
This may have morphed into the 12-string inline chromatic soron.
Which in turn may have morphed into the 21-string kora
The kamel n'goni is a popularized version of the doson n'goni, which is reserved exclusively for hunters.
I currently play on a 12-string kamel n'goni and one can easily find 6, 8, or 10-string instruments all over. I actually play with both kamel n'goni and kora technique and I currently have a 16-string harp being made that will combine construction techniques of the two instruments. This allows me to tune to 3 pentatonic octaves, or 2 full octaves in chromatic.
Please don't confuse the jeli n'goni (a spike lute plucked and fretted like a guitar) with the kamel n'goni ( a lute-harp played with harp technique). Very different instruments from very different groups. In Senegal and Mauritania the jeli n'goni is called the Xalam (Halam - hard H).
You can hear my band playing the two together on a couple tracks.
www.vagabontribe.com.