You want List::GetRange(firstIndex, count).

// I have a List called list
List sublist = list.GetRange(5, 5); // (gets elements 5,6,7,8,9)
List anotherSublist = list.GetRange(0, 4); // gets elements 0,1,2,3)

Is that what you’re after?

If you’re looking to delete the sublist items from the original list, you can then do:

// list is our original list
// sublist is our (newly created) sublist built from GetRange()
foreach (Type t in sublist)
{
    list.Remove(t);
}