1. Balfour-Browne, F., “British Water Beetles”, 3 (Ray Society, London, 1958).
2. Gilmour, J. S. L., Nature, 181, 379 (1958).
3. Ramsbottom, J., Proc. Linn. Soc. Lond., 150, 192 (1938).
4. Poulton, E. B., Proc. Ent. Soc. Lond., 1903, 77 (1904).
5. Mayr, E., “Systematics and the Origin of Species from the View-point of a Zoologist” (Columbia Univ. Press, New York, 1942).