23 



Fig. 10. Rhizosolenia minima , (k), cells h~ J\i in diameter, 



15 -^Ou long (excluding spines). X 350. Southwestern 

 U. S. (Red River). 



girdle view 



Notes : 



kb 



Two long spines arising from each valve - ATTHEYA 



Fig. 11. Attheya Zacharias i , (lQ ) , cells 12-40u in diameter; 

 spines k0-6O\i long. X 500. In Ohio and Tennessee 

 Rivers . 



girdle view 



Notes 



5a Valves with two marginal protuberances or horns on opposite 

 sides of the valve; usually seen in girdle view - BIDDULPHIA 



