так?:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
<html> <head>
</head>
<body>
<table>
<tr><td>1</td></tr>
<tr><td>1</td></tr>
<tr><td>1</td></tr>
<tr><td>1</td></tr>
<tr class="selected"><td>1</td></tr>
<tr><td>1</td></tr>
<tr><td>1</td></tr>
<tr class="selected"><td>1</td></tr>
<tr><td>1</td></tr>
<tr><td>1</td></tr>
</table>
<script type="text/javascript" src="http://code.jquery.com/jquery-1.10.2.min.js"></script>
<script type="text/javascript">
console.log($('tr.selected').eq(0))
</script>
</body>
</html>