NOMENCLATURE. 33 



Valv^. Valves. 



aquilateriB. ^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 rig-ht 

 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. 



