9 



GENERIC KEY 



la Valves with true raphe or pseudoraphe; ornamentation 



transverse and/ or longitudinal 8 



lb Valves without true raphe or pseudoraphe; ornamentation 



radial about a central point 2 



2a Frustules usually united into long filaments 



Melosira (p. 19) 



2b Frustules not usually united into long filaments; usually 



solitary but may form short chains 3 



3a Frustules with intercalary bands; usually seen in girdle 



view; one or two long spines arising from each valve.... k 



3b Frustules without intercalary bands 5 



ka. One long spine arising from each valve 



Rhizosolenia (p. 22) 



kh Two long spines arising from each valve. . . . Attheya (p. 23) 



5a Valves with two marginal protuberances or horns on 



opposite sides of the valve; usually seen in girdle view. 



Biddulphia (p. 23) 



5b Valves lacking protuberances 



6a Valve margin with costae; ornamentation in central area 

 different from margin Cyclotella (p. 2k ) 



6b Valve margin otherwise; central area not sharply distinct 

 from margin; valves with radial rows of punctae or with 

 geometric facets 



