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The behavior of the beach clam, Donax variabilis, resembles that of Donax semigranosis in that it migrates up and down the beach with the rise and fall of the tide assisted by the wash of the surf. On the rising tide the acoustic shock of the breaking waves stimulates the bivalve to emerge from the sand in advance of the uprush so that the wash carries it up the beach. On the falling tide it ignores the acoustic stimulus and emerges into the backwash to be carried down the beach. The reactions may be due to an intrinsic rhythm, changes in the water content of the sand, or a trigger‐and‐memory mechanism.

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