Hi Linda,
I'll see what I can figure out; I'm an amateur's amateur. But I can
recommend trying the book Sea Shells of Tropical West America by Myra
Keen (Stanford University Press, c. 1971). I've been using it to id
shells I found in Puerto Vallarta in March; it's helpful because it
has stuff not in the Compendium everybody talks about. If your local
library doesn't have it, maybe they can borrow a copy through their
Interlibrary Loan Dept. Hope this helps!
Sue in Denver