NOMENCLATURE. 33 



ValvjE. Valves. 



aquilatera. ^Equilateral ; where the anterior and 

 posterior sides of the valve are equal and 

 similar. — Inaequilateral ; the reverse. 



aquivalves. iEquivalve : where one valve is per- 

 fectly similar to the other. 



dextra et sinistra. Right and left. If the shell be 

 placed upon its base, with the area in front, 

 and the valves be then divided, the right 

 valve will be opposite the left hand of the 

 examiner, and the left valve opposite his 

 right hand. 



lacunosa. Lacunous ; marked with a longitudinal 

 depression. 



prominentes. Prominent; when one valve pro- 

 trudes in any part beyond the other. 



Umbones. Bosses; the swelling parts near the 

 beaks, the highest extreme of which, or 

 that point furthest removed from the base, 

 we consider as the summit. 



fornicati. Arched ; inwardly much excavated. 



