Shell Growth and Structure of Planktonic Foraminifera.
Planktonic foraminiferal tests show bilamellar additions to each chamber and develop a "secondary thickening" in the form of a calcite crust in late ontogeny. The evidence presented indicates that additional calcium carbonate is deposited upon the original bilamellar test and that maximum calcite crust thickness is attained at depths greater than 500 meters.
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