EXPLANATION OF TEEMS. 



Acephalous. Mollusca without an apparent head ; comprehending the 

 Bivalves of conchologists. 



Acuminated. Ending in a graduated, and often acute, point. 



Adductor Muscle. That which closes the two pieces of a Bivalve 

 together, the base or insertion of which is indicated by an irregular 

 depression in each valve, these being called the muscular im- 

 pressions. (See Muscular Impressions.) 



Annulated. Marked with rings. 



Anteally. In front, forward. 



Anterior. The side of the shell, in Bivalves, where the ligament is 



situated. (See Posterior.) 

 Aperture. The mouth or opening of the shell in Univalves, from 



which the head of the animal protrudes. 

 Apex. The commencement or top of the spire in Univalves. 

 Apical. Belonging to the apex. 

 Apophysis. The projecting, soft end of a bone. 

 Area. A flat space. 

 Articulated. Jointed. 



Auriculated. (Eared.) A term given to a few Bivalves which have 

 a flat angulated projection on one or both sides of the umbones 

 or bosses : these processes are most developed in the Pectens. 



Auriform. (Ear-shaped.) Shaped like an ear ; as the Haliotis. 



Axile. Belonging to the axis, or middle. 



Base. The extremity opposite to the Apex, in Univalves: in such 

 Bivalves as adhere to other substances by one of their valves, as 

 in Spondylus, Chama, &c, that valve is termed the basal. 



Bicarinated. Having two elevated or sharp ridges. (See Carinated.) 



Bicornute. Like, or having two horns. 



