shell ID help please

[caddymanlasalle]

i recently came back from Hawaii and have been trying to find out what this is called. it is the most strange shell i have ever seen or felt.
<a href="http://i829.photobucket.com/albums/zz219/caddymanlasalle/shells/IMG_0667.jpg" target="_blank"><!-- m --><a class="postlink" href="http://i829.photobucket.com/albums/zz219/caddymanlasalle/shells/IMG_0667.jpg">http://i829.photobucket.com/albums/zz21 ... G_0667.jpg</a><!-- m --></a>
<a href="http://i829.photobucket.com/albums/zz219/caddymanlasalle/shells/IMG_0668.jpg" target="_blank"><!-- m --><a class="postlink" href="http://i829.photobucket.com/albums/zz219/caddymanlasalle/shells/IMG_0668.jpg">http://i829.photobucket.com/albums/zz21 ... G_0668.jpg</a><!-- m --></a>

[xbonet]

podria ser ?

Colobocentrotus atratus