28 NOMENCLATURE. 



posticus. Posterior ; next the areola. 



complicates. Complicated ; membranaceous form- 

 ing an acute angle. 



duplicates . Duplicate ; deeply cleft, approaching 

 to bifid. 



depressus. Depressed ; turned inward. 



erectus. Erect ; perpendicular to the plane of the 

 hinge. 



longitedinalis. Longitudinal ; produced along the 

 margin. 



masticans. Articulate ; furnished with many teeth, 

 so situated that when the valves are closed 

 they lock into each other. 



primarius seu cardinalis. Primary or Cardinal ; 

 situated between the beaks. 



Discus. Disk ; the middle of each valve, the 

 convex part between the bosses and the 

 margin. 



Fossula. Sinus; a small hollow in the hinge. 

 Foveola and Scrobicalus have nearly the 

 same signification. 



Intestinum. Intestinal ligature ; a mem- 

 branaceous tube by which some of the 



