PLATE LI. 



FIGS. PAGE 



1. Micrasterias cornuta Benn. x 200 (after Bennett) 124 

 2. M. verrucosa Bissett. x 200 (after Bissett) . 109 

 3-6. If. Thomasiana Archer. 3 and 4, x 200 (after 

 Archer) ; 5, x 400; 6, basal view of semi- 

 cell with reduced processes, x 170 .110 

 7. An intermediate form between M. Thomasiana 



and M. denticulata. x 170 112 



