HOW TO KNOW THE FRESH-WATER ALGAE 

 183b Cell shaped differently, or not with such appendages 184 



184a With several long spines forming a tuft at the angles of the cell. 

 (See Polyedriopsis quadrispina, however) at the angle of the cell. 

 Fig. 129 POLYEDRIOPSIS 



Fig. 129. Polyedriopsis spinulosa G. M. 

 Smith. 



There are 2 species in this genus, 

 both of which are euplanktonic. They 

 are rectangular or polyhedral in shape 

 Figure 129 with from 1 to 4 long spines at each 



angle. P. quadrispina G. M. Smith 

 has but 1 stout spine at each angle; is quadrate in shape. 



184b With 1. 2, or 3 spines, or without spines at the angles of the 

 cell 185 



185a Without spines 186 



185b With 1-3 spines at the angles 187 



186a Body of the cell gradually narrowed at the angles to form horn- 

 like, twisted processes. Fig. 130 CERASTERIAS 



Fig. 130. Cerasterias irregulare G. M. Smith. 



There is apparently only 1 good species in 

 this genus which is characterized by having ir- 

 regularly triangular cells with twisted processes. 

 Occurs in the euplankton. Should be compared 

 with Tetraedron (Fig. 131). 



Figure 130 



86 



