1. Sherlock, Mem. Geol. Survey, Mineral Resources of Great Britain, Rocksalt and Brine, 18, 54 (1921).
2. Ormerod, G. W., Quart. J. Geol. Soc., 4, 269 (1848).
3. Ward, H. B., and Whipple, G. C., "Fresh-water Biology", 80 (1918).
4. Carpenter, K. E., "Life in Inland Waters", 228 (1928).
5. Thorpe, W. H., Trans. S.E. Union Sci. Soc., 27–34 (1927).