A detailed description of the procedure used in taking stream bottom samples follows a description of the stream square foot bottom sampler, which, although pictured in a publication by the author in 1937, was not described in detail in any publication. One of the principal problems in retrieving bottom animals from samples is getting them quickly from the gravel without damaging them. Large stones in the sample area are removed first and placed in a pail half-filled with water. The contents of the net are also emptied carefully into the same pail. Upon reaching the shore, the pail is filled with water. After washing and removal of the large stones which are placed where animals crawling from hiding places on them can be retrieved, a series of decantations are made into a U. S. Series No. 30 soil sieve 8 inches in diameter and 2 inches deep held in water above the screen surface. After this decantation process, the gravel and sand are placed in a white enamel photographic tray from which any molluscs present are removed. The few bottom animals that escape the decantation process are retrieved at this time. Animals and debris retained by the sieve are concentrated by a swirling action of the sieve and placed in pint jars. In the laboratory, the samples (after washing to remove formalin) are placed in large white trays, the bottoms of which have been divided into approximately 50 x 30 m.m. rectangles with a diamond point glass-marking pencil. The surface scratches are filled with India ink. Black, hard-rubber trays are used for the retrieval of animals in samples containing small oligochaete worms. Petri dishes about 100 m.m. in diameter are used for the systematic placement of bottom organisms within concentric circles spaced about 12 m.m. apart. The contents of the petri dishes are examined on the raised ~tage of a binocular microscope.
