70 



32b Raphe not enclosed in a siliceous rib. 



33 



33a Valves with chambered striae appearing as heavy costae; valves 



usually with parallel sides and broadly rounded poles - PIHNULARIA 



Fig. 105. Pinnularia borealis , (5), cells 20-110u long, 8-l8u wide; 

 k-6 striae in lOu. X 1000. 



valve view 



Notes : 



Fig. 106. Pinnularia gibba , (5), cells 50-llj-Ou long, 7-l8|J wide; 

 wide axial area and broad capitate ends. X 1000. 



valve view 



Notes 



33b Valves with striae appearing otherwise, 



3^ 



3**-a Central area extending laterally to the margins of the valve, 



striae absent along lateral margins of the central area - STAURONEIS 



