Display Pages with addition tag

I use wp_list_pages('title_li=') to make a page list such as

<ul>
 <li class="pagenav">
  <ul>
  <li class="page_item"><a herf="...">Pages Name</a></li>
  </ul>
 </li>
</ul>

but I can’t find the way to display it as this style

<ul>
 <li class="pagenav">
  <ul>
  <li class="page_item"><a herf="..."><span>Pages Name</span></a></li>
  </ul>
 </li>
</ul>

the tag I want to add is <span> before the Pages Names.
Please help me!