The selection of N. gibbosulus in Mediterranean web-sites and N. kraussianus is South African sites is a function of their availability within the vicinity in the internet sites, but doesn't describe why this genus was chosen about other shells of comparable size and shape. A comparison of your morphological characteristics https://medium.com/@spoilmevintagediy/the-rich-history-of-beadwork-a-journey-through-the-ages-4e4fd2e474cf