Fresh-Water Biology, 2'nd ed.
By H. B. Ward and G. C. Whipple, edited by W. T. Edmondson
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Review excerpt:
"In essence, the book is now a series of illustrated keys for identification. each key being preceded by supplementary information essential to its use. These keys, with a few exceptions. are easily followed by the nonspecialist and in most instances may lead the student to a generic identification, although frequently specific determinations can be made."