References
Thiele, J., 1929-1935. Handbook of Systematic Malacology, Vol. 1, Part 2 (Gastropoda: Opisthobranchia and Pulmonata). Translated from German by J.S. Bhatti. Bieler, R. & Mikkelsen, P., eds. Smithsonian Institution libraries and National Science Foundation, 1992. 625 pp.