A. H.  Cooke, The Cambridge natural history, vol. 3. London,The Macmillan, Company, 1895, p. 586.

E. A.  Smith, ?On a collection of land-shells from Sarawak, British North Borneo, Palawan, and other neighbouring islands?, Proceedings of the Zoological Society of London, vol. 1895, pp. 97?127, 1895.