Illinois Natural History Survey - University of Illinois

Glossary

Knowledge of the following terms is important for understanding the species accounts.

Anterior end -- the shorter end of the shell as measured from the umbo; also considered the front end

Beak -- the raised part of the dorsal margin of the shell; also called the umbo

Beak cavity -- the depression or pocket on the inside of each valve leading into the beak

Beak sculpture -- the raised loops, ridges, or bumps on the umbo

Chevron -- a V-shaped marking

Compressed -- flattened or pressed together laterally

Concentric -- having a common center

Distal -- away from the center or origin

Dorsal -- referring to the top part of the shell where the hinge is located

Elliptical -- having the form of an ellipse, or oval

Elongate -- long or extended

Extirpated -- locally extinct

Growth lines -- darkened lines on the surface of the shell indicating periods of rest during growth

Hinge -- the elastic part of the shell that unites the valves along the top of the shell

Inflated -- swollen or expanded

Interdentum -- a flattened area between the pseudocardinal and lateral teeth

Iridescent -- exhibiting rainbow colors

Lateral teeth -- the elongated teeth along the hinge line of the shell

Left valve -- the left half of the shell when the dorsal edge or hinge is facing up and the anterior end is directed forward (away from the collector)

Nacre -- the interior layer of the shell, usually white, pink, salmon, or purple and iridescent

Oblong -- having the shape of or resembling a rectangle or ellipse

Ovate -- egg-shaped

Pallial line -- a linear depression on the inside of the shell

Periostracum -- the outside layer or covering of the shell

Plications -- folds

Posterior end -- the longer end of the shell as measured from the umbo; also considered the back end; also the end with the siphons, usually sticking above the stream bottom

Posterior ridge -- the ridge on the back half of the valve running from the umbo to the posterior ventral edge

Posterior slope -- the area along the dorsal part of the shell between the posterior ridges of the valves

Pseudocardinal teeth -- the triangular, often serrated, teeth located on the anterior-dorsal part of the shell

Pustule -- a bump or raised knob on the outside surface of the shell

Quadrate -- square

Right valve -- the right half of the shell when the dorsal edge or hinge is facing up and the anterior end is directed forward (away from the collector)

Serrated -- notched or grooved

Shell margin -- the circumference of a valve outline when laid flat; also known as the edge

Solid -- thick or heavy

Striated -- marked with lines or grooves

Sulcus -- a shallow depression or furrow on the outside surface of the shell

Truncate -- having the end shortened or squared off

Tubercle -- a pointed, rounded, or knoblike projection on the shell

Umbo -- the inflated dorsal part of the shell; also called the beak

Valve -- one of the two halves of the shell

Ventral -- referring to the bottom edge of the shell

 



Created 6/9/95 Last Modified 1/10/2002 cam



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