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MANUAL OF ZOOLOGY 



SECT. 



The shell is of simple conical form in the Limpets. In 

 most of the Gastropoda it is in the shape of a spiral (Figs. 

 1 60 and 1 6 1 ) with the turns or whorls usually in close contact 





FIG. 161. Longitudinal median section of the shell of Triton nodifems. 



with one another, the inner walls of the turns coalescing to 

 form an axial, hollow or solid column the columella. By 

 far the greater number of such spiral shells are dexlral, 



