[jQuery] table tbody tr:last td

hi

I've a Problem:

I have a table like this:

<table class="sortable" id="res">
<thead>
<tr>
<th>123</th>
<th>123</th>
<th>123</th>
</tr>
</thead>
<tbody>
<tr>
<td>123</td>
<td>123</td>
<td>123</td>
</tr>
<tfoot>
<tr>
<th>123</th>
<th>123</th>
<th>123</th>
</tr>
</tfoot>
</table>

Now I made this script:
$(document).ready(function() {
$("table tbody tr:last td").css("border", "none");
});

But that doesn't work. Does anybody know why?

thank you