62 



24a Valves with elongate central or terminal nodules . . . , 

 24b Valves without elongate central or terminal nodules, 



25 

 26 



25a Central nodule drawn out to at least half the length 

 of the valve - AMPHIPLEURA 



Fig. 90. Amphipleura pellucida , (8), cells 50-l40u long, 7-9u 

 wide; punctae delicate and difficult to see. X 1000. 



valve view 



Notes : 



25b Central nodule drawn out less than half the length of the 

 valve - FRUSTULIA 



Fig. 91. Frustulia rhomboides , (8), cells 50-l60u long, 20-30u wide. 

 X 1000. 



valve view 



Notes 



