The choice of N. gibbosulus in Mediterranean websites and N. kraussianus is South African websites is really a perform of their availability within the vicinity from the websites, but doesn't explain why this genus was preferred over other shells of comparable sizing and condition. A comparison on the morphological characteristics https://medium.com/@spoilmevintagediy/the-rich-history-of-beadwork-a-journey-through-the-ages-4e4fd2e474cf