butterfly-shaped shell with photos

[bardite]

In the past couple of weeks I found several shell fragments with an unusual shape.  I have lived on the coast in the Pacific Northwest (California/Oregon border) for 14 years and have never noticed shell fragments like these.  Hopefully, the photo posting works -- <a href="http://www.badongo.com/pic/4874771" target="_blank"><!-- m --><a class="postlink" href="http://www.badongo.com/pic/4874771">http://www.badongo.com/pic/4874771</a><!-- m --></a> and [urlhttp://www.badongo.com/pic/4874770[/url] .

Thanks for your help.