Thanks! I haven't seen "donut" beads from Africa in quite this color, tho the style is similar. The seller seems to offer detectorist finds. An even more similar lot of beads from same seller is

http://www.ebay.com/itm/VIKING-Ancient-Artifact-STONE-BLACK-BEADS-of-NECKLACE-Circa-700-800-AD-/322198850710?hash=item4b048c4c96:g:basAAOSwsTxXj4eJ

With some ebay sellers, tho, you never know whether their attributions are knowledgeable, or commercially motivated.

Perhaps there have been many sources of wound, large-holed beads like this over the centuries, and the ones I have are unrelated to the "German" (Dutch?) ones common in the Africa trade.