68 LESSON XI. 



LESSON XL 



Teacher. If any one were now to speak to 

 you of a Conus, what idea would the name call 

 up to your mind] 



Child. The name Conus would recall the 

 idea of a univalve shell, whose form is inversely 

 conical and turbinate ; the spire retuse ; whorls 

 spirally convoluted, aperture linear, longitudinal, 

 entire, effuse at the base ; its columellar lip 

 smooth, having sometimes a few oblique rugose 

 striaB towards its base. 



Teacher. Yes, all the shells before us pos- 

 sess these qualities, or they would not be 

 Cones : -but are they alike in all respects ? 



Child. No ; they differ very much in their 

 colours and patterns, and also in their size. 



Teacher. On account of this variety in the 

 shells possessing the same generic marks, the 

 different genera have been subdivide^ into spe- 

 cies, the characters of which are determined by 

 the circumstances of colour, markings, size, and 

 the inequalities of the surface. Here is a shell 

 called Conus marmoreus : I wish you to examine 

 it, and draw out its specific character ; it is con- 

 sidered as the type or representative of the Co- 

 nus, from its having the characteristics of the 

 genus strongly marked. Now, tell me what you 

 have to do. 



Child. We must try and describe this shell. 



Teacher, Yes ; but you must recollect that 

 they are the specific distinctions only, that yoa 



