2k 



Fig . 12. Biddulphia laevis , (10), cells 20-150n in diameter, 

 50-150H long; X 650. Southwestern U. S. 





is 







valve view 



girdle view 



Notes : 



5b Valves lacking protuburances 



6a Valve margin with costae; ornamentation in central 

 area different from margin - CYCLOTELLA 



Fig. 13. Cyclotella atomus, (3), cells h-5i± 

 in diameter; every 5th or 6th 

 costae is thicker and darker than 

 the others; single ocellus in 

 central area. X 1500. Widely 

 distributed. 



valve view 



Notes 



Fig. lk. Cyclotella antiqua , ( k) , cells 



10-30(i in diameter; wedge-shaped 

 depressions in central area. 

 X 1200. In Great Lakes. 



valve view 



Notes : 



