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NOMENCLATURE. 
Lunula. Lunule; a small crescent-shaped 
depression on either the area or areola. 
Margo. Margin ; the outline or edge of the 
shell. 
Radii. Rays; See above. 
echinati. Spinous ; longitudinally armed with 
spines. 
vesiculares. Vesicular; beset with knots, or pro- 
minences internally concave. 
Rima. Suture; the interstice which separates 
the valves when the ligament is wanting, 
or the hollow which is covered by the 
ligament. 
clausa. Closed ; the internal lips being thickened 
so as to cover the whole suture. 
SguAMULAi. Scales. 
canaliculate^. Channelled ; excavated longitu- 
dinally. 
fornicatcc. Arched ; concavo-convex. 
imbricatcc. Imbricated ; laid partially over one 
another, like the tiles on a house. 
tuhulosec. Tubulous ; having the sides folded 
together so as to form a tube. 
