- British Library, The: BL Add. 46434 ff. 49-50
- Marchant, J. (Ed.). (1916). In: Alfred Russel Wallace; Letters and Reminiscences. Vol. 1. London & New York: Cassell & Co. [p. 160]
A congratulatory letter from Darwin to ARW about 2 of his papers he had sent Darwin; one on parrots and the other on geographic distribution.