Unique specimen , please help identify

[paul monfils]

This is an operculum from Astraea undosa (also known as Megastraea undosa), a large species found from southern California through western Mexico. If you are not familiar with "operculum", it is the "door" like structure that many snails use to close the aperture of their shell when they withdraw inside. Here's a picture of the shell: http://www.gastropods.com/2/Shell_292.shtml The shell at the bottom has the operculum in place.