SECTION Vir. 14^ 



However, they cannot be properly called 

 fimple, or Shells that are noways fpiral ; 

 becaufe at their head they have as perfect 

 and fine a whirl as any other turbinated 

 Shell : but, as Nature in her works has madi 

 fuch (light tranfitions from one family to 

 another, it is impoffible to fix them by hu- 

 man definitions. Thus feveral of the 

 Chambered Limpets have fuch fingle whirls, 

 and the Trocho Lepas and Cochlea Lepas 

 are even fo greatly fpiral, as exteriorly to 

 refemble a Trochus or a Snail ; yet are 

 they true Limpets. It is therefore im- 

 poiTible to regulate natural objefls to a per- 

 fefl: precifion, by the mod: elaborate and 

 minute definitions. 



This fpiral head of the Haliotis has 

 made fome authors not only feparate them 

 from the Limpets, but alfo ev^en rejeft 

 them from the fimple Shells. Thus 

 Lifter * places them in his HiPcoria Con- 



* See the note uhich is printed in p. 144. 



L chyliorum 



