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EXPLANATION OF TJ3RMS. 



Acephala. Without a head from the Greek 

 K<paXv) (cephale) a head. 



Apex. In univalve shells, the top of the spire. 



Apices. The plural of apex. In bivalve shells, 

 the points over the hinge : called also 

 the Beaks. ; 



Aperture. The entrance or opening of the shell. 



Auricula. Small earlike appendages placed at 

 the sides of the hinge of some bivalve 

 shells : the diminutive of auris, an ear. 



Area, or Anterior slope. The side of the beaks 

 where the ligament is situated. 



Areola, or Posterior slope. The side of the 

 beaks opposite to that where the liga- 

 ment is placed. 



Articulated. Having joints ; from articul us, a 

 joint. 



Annulated. Marked with rings ; from annul us. 

 a ring. 



Alatce. Winged ; from ala, a wing. 



Adductor Muscle. The muscle that closes the 

 valves ; from adduce, I bring together. 



Base. In univalve shells, the extremity oppo- 



