Subconical—less thanconicalin shape; almost a cone.
Suture—the line of junction between two parts; in crinoids, the line of junction between two plates; in gastropods, the line of junction of the whorls as seen on the exterior of the shell; in cephalopods, the line of junction between aseptumand the shell wall.
Symmetry—orderly arrangement of parts of an object with reference to lines, planes, or points.
Bilateralsymmetry—the symmetrical duplication of parts on each side of a vertical anterior-posterior plane.
Radial symmetry—the symmetrical repetition of parts around a common vertical dorso-ventrally disposed axis.
Pentameroussymmetry—symmetry arranged in a pattern of fives.
System—the rocks formed during aperiod; the time-stratigraphic term next in rank above aseries.
Taxonomy—that branch of science that deals with classification, especially in relation to plants, animals, or fossils.
Tertiary—the oldestperiodof theCenozoicera; follows theCretaceousperiod of theMesozoicand precedes theQuaternaryperiod of the Cenozoic.
Test—the protective covering of some invertebrate animals.
Theca—a sheath or case; in coelenterates, the bounding wall at or near the margin of theexoskeleton; in echinoderms, the main body skeleton (orcalyx) which houses the animal’s soft parts; in graptolites, any cup or tube of the colony.
Thorax—in trilobites, that part of the body between thecephalonand pygidium.
Time-unit—a portion of continuous geologic time (e.g., eras, periods, epochs, and ages).
Time-rock unit—same as time-stratigraphic unit.
Time-stratigraphic unit—term given torockunits with boundaries established by geologic time; strata deposited during definite portions of geologic time (e.g., systems,series, stages, etc.).
Topography—the physical features or configuration of a land surface.
Topographic map—a map showing the physical features of an area, especially the relief and contour of the land.
Transverse—at right angles to length.
Triassic—the youngestperiodof theMesozoicera; follows thePermianperiod of thePaleozoicand precedes theJurassicperiod of the Mesozoic.
Trilobite—an extinct marine arthropod having a flattened segmented body covered by a hardeneddorsalexoskeletondivided into three lobes.
Trivial name—the Latinized name added to a generic name to distinguish thespecies; same asspecific name.
Type locality—the geographic location at which aformationwas first described and from which it was named; or from which the type specimen of afossilspeciescomes.
Type specimen—the individual or specimen on which the original designation of aspecieswas established.
Umbilicus—an external depression or opening at the center of many loosely coiled shells; in gastropods it is usually located at the base of the shell; in cephalopods it is usually located laterally.
Umbo—the arched part of thevalvenear the beak in bivalve shells.
Unicellular—composed of one cell.
Valve—the one or more pieces comprising the shell of animals.
Variety—a subdivision of aspecies, designated by a third name when avarietyis designated.
Ventral—pertaining to the abdomen; as opposed todorsal, pertaining to the back.
Vertebrate—an animal having a backbone or spinal column.
Whorl—a single turn or volution of a coiled shell.
-zoic—combining form meaning “life” (Greekzoikos, life).
Zooecium(plural,zooecia)—tube or chamber occupied by an individual of the bryozoan colony; also called an autopore.
[1]Associate Professor of Geology, Lamar State College of Technology, Beaumont, Texas.[2]Entries marked with asterisk are published by the Bureau of Economic Geology, The University of Texas, Austin. Those not out of print are distributed at nominal sale price; list sent on request. These publications may be consulted at many public libraries and/or Chamber of Commerce offices.
[1]Associate Professor of Geology, Lamar State College of Technology, Beaumont, Texas.
[2]Entries marked with asterisk are published by the Bureau of Economic Geology, The University of Texas, Austin. Those not out of print are distributed at nominal sale price; list sent on request. These publications may be consulted at many public libraries and/or Chamber of Commerce offices.
Page numbers in italics indicate illustrations.
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