38 



12b Frustules without bulbous ends, typically not forming 

 stellate colonies 



13 



13a Valves symmetrical about the transapical plane Ik 



13b Valves asymmetrical about the transapical plane - OFEPHORA 



Fig. ^3. Opephora Martyi , (h) , cells 5-60u long, k~8\i wide; X 1000. 



valve view 



girdle views 



Notes : 



lk& Frustules typically forming ribbon-like chains, rarely 

 solitary - FRAGILARIA 



Fig. hk. Fragilaria arcus , (5), cells 15-150u long, l)-7u wide; 15-18 

 striae in lOu; cells swollen on the concave side near the 

 central area. X 1000. Abundant in the Delaware and 

 Columbia Rivers. 



eOgggSSSSSSSS^^ 



valve views 



Notes: 



