JQuery :: How To Use (This) To Isolate Interaction

I will have multiple li's of the same structure below on the same page. I click "more" and then the overlay appears. The only issue is that it appears for each instance. I understand why but I don't understand how to use the $(this) to isolate the interaction.

<li class="marketingItem">
<div class="thumb">
<?=img(array('src'=>'images/marketing/gil.jpg','alt'=>'Book 1'))?>
<div>
<div class="overlay">
lorem ipsum overlaysum.
</div>
<div class="title">
This is the Title<br />
<a href="#" class="more">more</a>
</div>
</li>

<script type="text/javascript">
$(document).ready(function(){
$('.more').click(function(){
$('.overlay').toggle('slow');
});
});
</script>