jquery-ui - selectmenu: How to set a specified number of items to show?

Question

I am using Jquery ui 1.11.4 and its selectmenu to display a select list with about 200 items.

<select id="myselect">
    <option>1</option>
    ...
    <option>200</option>
</select>

I would like it show only 40 items plus a scrollbar. I tried the following, but it is not working:

<style>
  .overflow { height: 200px; }
</style>


$( "#myselect" ).selectmenu({}).addClass( "overflow" );

Currently, the menu, when it opens, is a long list showing all items.

How can I make it show 40 items only?

Thanks!