:first-of-type Selector
Selects all elements that are the first among siblings of the same element name.
.first-of-type()
The :first-of-type
selector matches elements that have no other element with both the same parent and the same element name coming before it in the document tree.
Find the first span in each matched div and add a class to it.
JS
<div>
<span>Corey,</span>
<span>Yehuda,</span>
<span>Adam,</span>
<span>Todd</span>
</div>
<div>
<b>Nobody,</b>
<span>Jörn,</span>
<span>Scott,</span>
<span>Timo</span>
</div>
CSS
span.fot {
color: red;
font-size: 120%;
font-style: italic;
}
HTML
$("span:first-of-type").addClass("fot");
DEMO