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Brown, Thelma F. 



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1937. Productivity of a land snail, Polygyra thyroides (Say). Ecology, 

 vol. 18, pp. 545-546. 

 Foster, T. D., and Van Cleave, H. J. 



1937. The seasonal life history of a land snail, Polygyra thyroides (Say). 



Nautilus, vol. 51, pp. 50-54. 

 Truog, E. 



1938. Soil acidity and liming. U. S. Dept. Agr. Yearbook for 1938, pp. 



563-580. 



