Coelenterate—invertebrates characterized by a hollow body cavity, radial symmetry, and stinging cells; a member of phylum Coelenterata; includes jellyfishes, corals, sea anemones. Colonial—in biology refers to the way in which some invertebrates live in close association with, and are more or less interdependent upon, each other; colonial corals, hydroids, etc. Columella—a small column or central axis; in corals the small rod or axial pillar in the center of the corallite; in gastropods the solid or perforate pillar formed by the union of the successive coils of a conispiral shell. Columnal—one of the disk-shaped segments of a crinoid stalk. Concentric—having a common center, as circles; refers to shell markings that are parallel to shell margin. Concretion—nodular or irregular masses in sedimentary rocks and usually formed around a central core, which is often a fossil. Conical—cone-shaped. Conodont—minute tooth-like fossils found in certain Paleozoic rocks; their origin is not definitely known, but they may have been part of some type of extinct fish. Coral—bottom-dwelling marine invertebrate that secretes calcareous hard parts; member of class Anthozoa, phylum Coelenterata. Corallite—the skeleton formed by an individual coral animal; may be solitary or form part of a colony. Corallum—the skeleton of a coral colony. Corona—crown; in echinoids the main part of the skeleton consisting of symmetrically arranged calcareous plates. Coprolite—the fossil excrement of animals. Correlation—the process of demonstrating that certain strata are closely related to each other or that they are stratigraphic equivalents. Cretaceous—the third and last period of the Mesozoic era. Cystoid—an extinct stemmed echinoderm with calyx composed of numerous irregularly arranged plates; member of class Cystoidea. Dendritic—resembling a tree, branching. Dentition—the system or arrangement of teeth peculiar to any given animal. Devonian—the fourth oldest period of the Paleozoic era, follows the Silurian, precedes the Mississippian. Dip—the angle of inclination which the bedding plane of rocks makes with a real or imaginary horizontal line. Distillation—in fossils that process by which volatile organic matter is removed, leaving a carbon residue. Dolomite—a mineral composed of calcium magnesium carbonate (CaMg(CO₃)₂). Dorsal—pertaining to the back. Echinoderm—a marine invertebrate with calcareous exoskeleton and usually exhibiting a five-fold radial symmetry; member of phylum Echinodermata; includes cystoids, blastoids, crinoids, starfishes, and sea urchins. Echinoid—bottom-dwelling, unattached marine invertebrate with exoskeleton of calcareous plates covered by movable spines; member of class Echinoidea; sea urchins, heart urchins, biscuit urchins. Endoskeleton—the internal supporting structure of an animal.