I don't have "Jewels of a Continent" at hand, but it is possible that the ones featured there were found in Nigeria. The Picard site image linked by Rosanna above
http://www.picardbeads.com/trade_beads/ni3.html
shows beads sourced in Zaire similar to the Khond ones Joan and Hendrik show. But they are different. The Khond (used by the Chin) examples are more refined, and more graceful and tapered at the ends. I have seen both versions, they are quite different, yet similar!