The circular vibratory screener consists of two screening decks, one above the other, with an imbalanced-weight gyratory motor that causes them to vibrate. "When the time comes to remove the larger clams from a raceway, we scoop several handfuls of them into the top deck of the screener, which has a slightly larger mesh than the lower one," Mayer explains. "For example, we might have a 3/8 in. (9500 micron) screen on top and a 1/4 in. (6300 micron) screen on the bottom. As the clams move toward the periphery, the smaller clams fall through onto the bottom screening deck. Those small enough to pass through the tighter mesh of the lower screen are ejected through a discharge spout into a collection pan. Those too large to pass through the smaller mesh are ejected through another discharge port into a separate collection pan. The largest clams, those that failed to pass through the larger mesh of the upper screen, remain on that screen."