Part 35

Respiration—the process of oxygenation.

Rock—an aggregation of one or more minerals.

Rock-unit—divisions of rocks based on definite physical and lithologic characteristics and not defined on the basis of geologic time alone; groups, formations, members.

Rudistid—a Cretaceous pelecypod that does not exhibit the typical clam or oyster shape; many are cone-shaped, resembling corals.

Saddle—in cephalopods, the forward flexure (curved toward the aperture) of the suture or septum.

Scaphopod—an exclusively marine mollusk with a single-valved tusk-shaped shell; member of class Scaphopoda, phylum Mollusca.

Scavenger—an animal that feeds on organic refuse.

Sedentary—stationary in life, not moving from place to place.

Sediment—material that has been deposited by settling from a transportation agent such as water or air; typically composed of weathered rock fragments.

Sedimentary rock—rocks formed from the accumulation and lithification of sediments.

Segment—one of the parts into which a body naturally separates or is divided; for example, segments of arthropods or annelid worms.

Septal—pertaining to the septum.

Septum (plural, septa)—a dividing wall or partition; in fusulinids, a partition between chambers in the fusulinid shell; in corals, one of the radiating, longitudinal, calcareous plates located within the corallite; in cephalopods, the transverse partitions between the chambers.

Series—the rocks formed during an epoch; the time-stratigraphic term next in rank below a system.

Serrate—notched like a saw.

Sessile—animal attached to the sea floor more or less permanently.

Silica—an oxide of silicon (SiO₂).

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.

Stratum (plural, strata)—a single bed or layer of rock.