11 



13a Valves symmetrical about the transapical plane lk 



13"b Valves asymmetrical about transapical plane 



Opephora (p. 38) 



l4a Frustules typically forming long ribbon-like chains, 



rarely solitary Fragilaria (p. 38 ) 



l^b Frustules typically solitary, sometimes forming stellate 



colonies; striae often appearing as costae 



Synedra (p. k2) 



15a Raphe evident on at lease one valve l6 



15b Raphe not evident, concealed in a keel or wing 35 



l6a Valves similarly ornamented, raphe on both valves 19 



l6b Valves not similarly ornamented, raphe on one valve, 



opposing valve with pseudoraphe, or with rudimentary 



raphe near valve poles 17 



17a Valves elliptical, never linear, sometimes bent along the 



apical axis Cocconeis (p. hj) 



17b Valves not elliptical, usually linear, and usually bent 



along the transapical axis 18 



l8a Valves symmetrical about the transapical plane, one 



valve with completely developed raphe, opposing valve 



with pseudoraphe Achnanthes (p. 50) 



l8b Valves asymmetrical about the transapical plane, one 



valve with completely developed raphe, opposing valve 



with rudimentary raphe near valve poles 



Rhoicosphenia (p. 52) 



