From Scott Semans (coincoin.com) I have that beads like this one are used by the brides-to-be of the Mandinka, to show they are about to marry and are waiting for their beloved (which is somewhere in the bush collecting more precious goodies for her).
They are made of jasper, and show pecked, very small, not strait perforations.
The speciment shown is 36,5 mm long,but I own several more, both larger and smaller.
As I am about to upload them to my web page, educated information would make me happy.