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472 Bimiey^s Monograph of the Helices 



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Section I. — Lip reflected. 



Comprising all those species the margin of the aperture 

 of whose shell is more or less reflected. -^ 



A. umbilicus^ wholly or partially covered. 



Containing species in which the centre of tlie base of the she!! 

 is wholly or partly covered by the reflection of tlie lip at its junc- 

 tion with the base. 



■4; 

 * Aperture destitute of tooth-like processes. 



** Aperture furnished with one or more tooth-like processes. 



B. umbilicus not covered* 



Containing species in which the centre of the base of the shel! 

 is not covered by the reflection of the lip, but in which the open 

 space, or imaginary axis about which the whorls of the shell 

 revolve, is more or less open and visible. 



*** Aperture destitute of tooth-like processes. 



Aperture furnished with one or more tootli-like processes. 



ff w H K 



Section 1L — Lip simple. 



Comprising all those species, the margin of the aper- 

 ture of whose shell is not in any degree reflected, although 

 it is sometimes a little thickened. The aperture, properly 

 speaking, is never furnished with teeth, but in some of the 

 species there are lamellar processes considerably within 

 the aperture. 



■■> 



•C. umbilicus closed. 



Containing species in which the whorls * revolve so closely 

 about the axis as ordinarily to leave no perceptible opening. 



D. umbilicus open. 



Containing species in which the whorls revolve in such a 

 manner as to leave a visible space between them, which in some 

 is minute, in others so ample as to exhibit nearlv all the volutions. 



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