help me with this littorinidae

[luigi_67]

Help me with this seashell, I founded on rocks mexican caribbean
is black and i think is a kind of littorinidae family

<a href="http://img151.imageshack.us/my.php?image=littorinidaenegrastf3.jpg" target="_blank"><img src="http://img151.imageshack.us/img151/8414/littorinidaenegrastf3.th.jpg" alt="http://img151.imageshack.us/img151/8414/littorinidaenegrastf3.th.jpg" style="border:0" /></a>

[paul monfils]

These are closely related to Littorinidae, but are actually in the family Planaxidae. Planaxis nucleus (Bruguiere, 1789)