Amalia von X
From Anecdotes about Nineteen Century Authors

`Amalia' was probably Melanie von Spiegel, `a Junoesque beauty', but may have been Jenny von Pappenheim. See Gordon N. Ray, Thacheray: The Uses of Adversity (New York, 1955), pp. 142-3.

Note from Thackeray, from Literary Anecdotes