26 NOMENCLATURE. 



atiriformes. Auriform ; ear-shaped, having an 

 incurvated arch between the beaks. 



corniformes. Corniform ; horn-shaped, long, pro- 

 duced, straight, mucronate, or pointed. 



iriftexi. Inflex; incurved, bending towards each 

 other. 



reftexi. Reflex ; turned towards the areola. 



spirales. Spiral ; twisted spirally. 



Auriculae. Ears; angular processes either on 

 one or on both sides of the beaks. 



Ba sis. 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. 



