18 NOMENCLATURE. 



Columella. Pillar ; the middle column about 

 which the wreaths form their spiral cir- 

 cuit. 



olrjipta. Abrupt ; truncate at the base. 



caudal a. Caudate ; elongated so as to project be- 

 yond the body. 



plana. Flat ; extending into a plain lip. 



plicala. Plicate ; marked with transverse folds. 



spiralis. Spiral ; caudate and spirally twisted. 



CosT^E. Ribs ; keel-like processes reaching from 

 the apex to the periphery of the shell. 



fornicatcB, Arched ; beset longitudinally with 

 hollow scales. 



DrGiTi. Claws; digitate or finger-like lobes of 

 the outer lip. 



Dorsum. Back ; the upper part of the body 

 when laid on the aperture. 



Epidermis. Skin; a membranaceous covering 

 of the shell, found on some but not on all 

 species. 



Genicula. Gkkiculations ; the contraction of 

 the whorls so as to correspond wit]\ the in- 

 ternal divisions or dissepiments. 



