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NOMENCLATURE. 
posticus. Posterior ; next the areola. 
complicatus. Complicated ; membranaceous form- 
ing an acute angle. 
duplicatus. Duplicate ; deeply cleft, approaching 
to bifid. 
depressus. Depressed ; turned inward. 
erectus. Erect ; perpendicular to the plane of the 
hinge. 
longitudinalis. 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. 
Di sc us. 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 Scrobiculus have nearly the 
same signification. 
Intestinum. Intestinal ligature ; a mem- 
branaceous tube by which some of the 
