58 LESSON X. 



equal breadth throughout, it is called linear, 

 from its having the character of a line. In con- 

 sidering the parts of an object, what besides 

 their form strikes your attention ? 



Child. Their position and direction. 



Teacher. You remember the usual position 

 of the aperture. 



Child. It is almost always dextral or on the 

 right side of the shell. 



Teacher. And as this is its usual position, it 

 is not noticed in the generic character, indeed 

 the peculiarity of a sinistral aperture never runs 

 through a whole genus of shells. But what do 

 you observe with regard to the direction which 

 the mouth of the Cone takes ? 



Child. It is in the direction of a line passing 

 from the apex to the base, that is the length 

 of the shell. 



Teacher. And what do you call the direction 

 of a line passing from the top of a body to its 

 base? 



Child. Longitudinal ; the aperture of the 

 Cone is longitudinal. 



Teacher. You recollect learning in a former 

 lesson the proper term for shells with a beak, 

 and also for those without one. 



Child. Yes, those with beaks are called 

 canaliculated, and those without entire. The 

 mouth of the Cone is entire. 



Teacher. Yes. A little experiment will lead 

 you to detect another characteristic of this 

 genus. Observe, I fill this shell (a Turbo) with 



