Part 34

Pedicle opening (pedicle foramen)—see Foramen.

Pelecypod—a bivalved aquatic invertebrate; member of class Pelecypoda, phylum Mollusca.

Pennsylvanian—the sixth oldest period of the Paleozoic era; follows the Mississippian, precedes the Permian.

Period—a division of geologic time (Pl. 1).

Periostracum—the horny outer covering or epidermis on shells.

Permian—seventh and last period of the Paleozoic.

Permineralization—that process by which mineral matter has been added to the original shell material by precipitation in the interstices rather than replacing the original shell material.

Phosphatic—containing or pertaining to phosphate minerals.

Phylum—one of the primary divisions of the animal or vegetable kingdoms.

Planispiral—shell coiled in one plane.

Pleistocene—earliest epoch of Quaternary period, Cenozoic era; follows Pliocene epoch of Tertiary period, precedes Recent epoch of Quaternary.

Pleural—referring to the side or ribs; in trilobites, refers to lateral portions of thorax and pygidium.

Pliocene—latest epoch of Tertiary period of Cenozoic era; follows Miocene epoch and precedes Pleistocene epoch of Quaternary period.

Polygonal—many sided or having many-sided plates.

Polyp—a many-tentacled aquatic coelenterate animal, typically cylindrical or cup-shaped, as in corals.

Porcelaneous—like porcelain.

Pore—a very small opening.

Posterior—situated behind; to the rear.

Precambrian—that portion of geologic time before the Cambrian; divided into Archeozoic era (Early Precambrian) and Proterozoic era (Late Precambrian).

Protero—combining form meaning fore, former, or anterior in time (Greek proteros, fore).

Proterozoic—youngest era of the Precambrian; follows the Archeozoic era and precedes the Cambrian period of the Paleozoic era.

Protista—the organic kingdom including the simplest of all one-celled organisms which possess various characters of both plants and animals; bacteria, algae, foraminifers, radiolarians.

Protoconch—in mollusks, the initial chamber of shell.

Pyrite—a hard, brass-yellow mineral composed of iron sulfide; “fool’s gold.”

Quaternary—the youngest period of the Cenozoic era, follows the Tertiary period.

Radial symmetry—see Symmetry.

Reef—a mound-like or ridge-like elevation of the sea bottom which almost reaches the surface of the water, composed primarily of organic material and commonly formed by reef-building animals, such as corals and oysters.

Replacement—type of fossilization whereby hard parts of organisms are removed by solution accompanied by almost simultaneous deposition of other substances in the resulting voids; mineralization.