5* 



19b Raphe fully developed, extending the length of the valves 20 



20a Valves symmetrical about both the transapical and 



apical plane 2k 



20b Valves asymmetrical about either the apical or transapical 



plane 21 



21a Valves symmetrical about the transapical plane, asymmetrical 



about the apical plane 23 



21b Valves asymmetrical about the transapical plane, symmetrical 



about the apical plane 22 



22a Valve margins with longitudinal "shadow"-lines - GOMPHONEIS 



Fig* 73* Gomphoneis herculeana , (ll), cells 30-136|i long, 12-22u 

 wide; 9-12 striae in 10u; central area rounded with an 

 isolated puncta. X 1000. 



valve view 



Notes 



22b Valve margins lacking longitudinal "shadow"-lines - GOMPHONEMA 



Fig. 7^. Gomphonema abbreviatum, (5), cells 7-3^ long, 2-6u wide; 

 19-22 striae in lOu. X 1000. 



^ 



valve view 

 Notes : 



