30 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. 



Squamul^. Scales. 



canaliculate. Channelled ; excavated longitu- 

 dinally. 



fornicatcc. Arched ; concavo-convex. 



imbricafce. Imbricated ; laid partially over one 

 another, like the tiles on a house. 



tubulosa. Tubulous ; having the sides folded 

 together so as to form a tube. 



