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NOMENCLATURE. 
auriformes. Auriform ; ear-shaped, having an 
incurvated arch between the beaks, 
corniformes. Corniform ; horn-shaped, long, pro- 
duced, straight, mucronate, or pointed. 
injiexi. Inflex ; incurved, bending towards each 
other. 
rejiexi. Reflex , turned towards the areola. 
spirales. Spiral ; twisted spirally. 
Auricula. Ears; angular processes either on 
one or on both sides of the beaks. 
Basis. Base ; that part of the margin which is im- 
mediately opposite to the beaks or summit, 
Cavitas. Cavity ; interior superficies of the 
shell. 
Callus. Callus ; composed, as it were, of two 
abbreviated ribs, united at the base, con- 
verging from the apex towards the poste- 
rior margin. 
Cardo. Hinge; that part of the circumference 
in which the valves cohere, or are attached 
to each other. It forms the thickest region 
of the shell, and is inwardly furnished with 
various protuberances and hollows. 
