Trochidae identification help

[shell collector de]

Hello shell collector

Enclosed you will find a picture of some shells I've found at one of Kenya's beaches.

<a href="http://www.putfile.com/pic.php?img=5646021" target="_blank"><img src="http://img2.putfile.com/thumb/6/16010554340.jpg" alt="http://img2.putfile.com/thumb/6/16010554340.jpg" style="border:0" /></a>

These shells are max. 10 mm high and 13 mm in diameter. They all have an umbilicus. I suppose these shells belong to the Genus Trochus. But I was not able to identify these shells clearly. Maybe you can help me.
Thank you.  <span class="petit">--Last edited by wolfgang.j.braun on 2007-06-10 16:57:46 --</span>