I found a very helpful thesis by Sunah Ahn a student at Rochester Institute of Technology RIT Scholar Works where she dissects the role and meaning of shells in different cultures, past and present.
I will talk about it more in my PDF, but you can access her work through this link:
http://scholarworks.rit.edu/cgi/viewcontent.cgi?article=7279&context=theses
Cloudiine 