ARCELLA. 113 



number ; it is found amongst Conferva, as well as 

 the next genus, Arcella, which differs in form, 

 being flatter, and the surface not covered with 

 sand. A. acideata has spines upon its surface, and 

 a large opening. A. vulyaris has the lorica round, 

 and covered with rows of minute granules, and 

 A. dentata is of a hemispherical form, and has 

 the margin dentated. The last genus of this 

 family, Cyphidium, has only one dilated process ; 

 the lorica is pitcher-shaped, with protuberances 

 upon it, which give it a square form : the pro- 

 cess by which it moves may be termed a foot, 

 and resembles the body of the genus Amoeba. 

 OypMdivm aureolum is the only species. 



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