Do I need to add callback=? or ?callback=? for my url to work using Jsonp

Do I need to add callback=? or ?callback=? for my url to work using Jsonp

I'm trying take the json response being returned from this web service and dump it onto a webpage. However  for now I was trying to simply start small and see if I could print out just the total.  Since nothings happy I'm sure there's something wrong, but I'm not sure where??? I'm assuming it's something to do with the url???

<!DOCTYPE html>
<html>
<head>
<script src="http://code.jquery.com/jquery-1.6.4.min.js"></script>
<script >
    $(document).ready(function($) {
    var url = 'https://www.sciencebase.gov/catalog/items?parentId=504108e5e4b07a90c5ec62d4&max=60&offset=0&format=jsonp';
 
    $.ajax({
        type: 'GET',
        url: url,
        jsonpCallback: 'getSBJSON',
        contentType: "application/json",
        dataType: 'jsonp',
        success: function(json) {
 
            $(this).show('json.total');
 
        },
        error: function(e) {
            console.log(e.message);
        }
    });
});
</script>
</head>
<body>
<form>
</form>
</body>
</html>