170 DESCRIPTION OF [Puiygastrica. 



another creature with three spines projecting from its 

 lorica, and a single variable process issuing from the under 

 side ; the digestive cells may also be seen. Fig. 94 shews 

 an empty deformed lorica. Diameter of lorica 1-2 10th. 



158. Arcella dentata. The toothed Arcella. — Lorica 

 membranous and homogeneous; of an hemispherical or 

 polygonal form, having the margin dentated ; colour 

 yellowish or greenish. Found amongst conferva. Size 

 1-5 70th to l-240th. 



159. Arcella? hyalina. The crystal Arcella. — Lorica 

 membranous, smooth, and approaching to globular, smaller 

 than the preceding ; colourless. Found in matter preci- 

 pitated from water, along with Cyphidium aureolum, &c. 

 Size 1-1 150th to 1-5 70th. 



Genus XLIIL Cyphidium. This genus is distin- 

 guished by the creatures having only one dilated variable 

 process, and a lorica of the form of a pitcher, with protu- 

 berances issuing from it. It forms a connecting group 

 between Arcella and Bacillaria, by reason of the simple 

 locomotive organ (like a snail's foot), and approaches very 

 closely to the group Desmidiacea. The lorica is some- 

 thing like a little die or stamp, mounted upon a short 

 stem. It is very irregularly formed, having protuberances 

 so as to make it appear four-corned ; it is combustible. 

 The organ of locomotion is a Inroad, gelatinous, variable 

 process, with smooth edges, resembling in appearance the 

 body of Amoeba verrucosa. Neither digestive cells or 

 apertures in the lorica have yet been observed, nor 

 systems of sensation or propagation. 



160. Cyphidium aureolum. The gold-coloured Cyphi- 

 dium. — Lorica of a cubical form, with protuberances ; 



