Siliceous—containing or pertaining to [silica].
Silicification—the process of combining or impregnating with [silica].
Silurian—the third oldest [period] of the [Paleozoic] era; follows the [Ordovician], precedes the [Devonian].
Sinus—an elongate depression on [brachiopod] shells.
Siphuncle—in cephalopods, the segmented horny or [calcareous] tube which extends from the [protoconch] to the living chamber.
Slickensides—polished and grooved surfaces that are the result of two [rock] masses sliding past each other as in faulting.
Solitary—living alone; not part of a colony.
Species—one of the smaller natural divisions in classification.
Specific name—see [Trivial name].
Spicule—a minute spike or dart, skeletal element in sponges and holothurians.