218 



EXPLANATION OF TERMS. 



Acephala. Without a head, from the Greek 



K<paXy (cephale) a head. 



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

 Apices. The plural of apex. In hivalve shells, 



the points over the hinge : called also the 



Beaks. 



Aperture. The entrance or opening of the shell. 

 Auriculae. 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 heaks 



where the ligament is situated. 

 Areola, or Posterior slope. The side of the beaks 



opposite to that where the ligament 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 opposite 



