Parse JQuery Serialized Data In C#?

I have a ListBox on my page. I'm making an AJAX call to a C# function, and I need to pass the values of the selected items. Here's what I have:

$('#btnSubmit').click(function() {
$.ajax({
type: "POST",
url: 'Default.aspx/GetSelectedValues',
data: '{selectedValues: ' + $('#lbItems').serialize() + '}',
contentType: "application/json; charset=utf-8",
dataType: "json",
success: OnSuccess
});
});
<select id="lbItems" multiple="multiple">
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
<option value="4">Four</option>
<option value="5">Five</option>
</select>
[System.Web.Services.WebMethod]
public static string GetSelectedValues(string selectedValues)
{
//
}

The data being passed to the C# function looks like:

lbItems=1&lbItems=3&lbItems=5

Is there any built-in C# function that can deserialize that easily, to convert the values into an array of some sort? Or maybe there's a better way to pass the data from jQuery?