Mollusca. 65 



6. The turns of the shell between the groove are the whorls. 



7. The whorls, taken together, make the spire. 



8. The lid closing the aperture is the operculum ; is this present 

 in all the snails you find ? 



9. Lay the snail shell beside a common screw ; if the whorls 

 turn like the threads of the screw, it is a right-hand, or dextral, 

 shell, if they turn the other way, it is a left-hand, or sinistral, shell. 



10. Make a drawing, naming all the parts, of the snail shell 

 with the aperture toward you ; with the aperture away from you ; 

 with the apex toward you. 



Read The Chambered Nautilus, Holmes. 



