Experienced aquatic biologists will be familiar with most organisms illustrated in Plates 1–40, and seldom will need the assistance of keys to identify organisms to the level illustrated. Because these plates are not intended for critical identification, specific (species) names are not generally cited. Organisms most likely to be observed are illustrated. For the convenience of those less familiar with the organisms referred to in preceding sections, a series of short keys is presented to enable them to identify most organisms to the level illustrated by the plates.
In conformity with preceding sections, organisms are arbitrarily divided into microscopic and macroscopic, depending on whether or not they pass through a U.S. Standard No. 30 sieve (0.5 mm). To study microscopic forms, use a compound or inverted microscope. To examine the smaller macroscopic organisms and to resolve the finer structures of larger forms, use a wide-field stereoscopic microscope.