yes, i know these beads but dont know any local or trading name for them- and also am most intrigued by the transparent middle zone- but dont have any more information than you have-

i'm confident they are Venetian and contemporary with the other lampwork beads intended for African trade, late 19th/early 20th C.
John Picard may know more because he has studied sample cards very methodically -and Jamey too of course-

good luck with your research, and please let us know if you find out more...