A truly amazing shell, like nothing i have ever seen

[ozzydan]

Hi
I found this unusual shell and have never seen anything like it. Yes it is a real shell. Anyone have any ideas as to what it may be. It was found around Sydney.
<a href="http://www.badongo.com/pic/2653548" target="_blank"><!-- m --><a class="postlink" href="http://www.badongo.com/pic/2653548">http://www.badongo.com/pic/2653548</a><!-- m --></a>
I have a link to more pics
<a href="http://www.badongo.com/pic/2653610" target="_blank"><!-- m --><a class="postlink" href="http://www.badongo.com/pic/2653610">http://www.badongo.com/pic/2653610</a><!-- m --></a>
<a href="http://www.badongo.com/pic/2653662" target="_blank"><!-- m --><a class="postlink" href="http://www.badongo.com/pic/2653662">http://www.badongo.com/pic/2653662</a><!-- m --></a>