Smithsonian Report, 1916. — Mann. 



Plate 6. 



'^SS^^^ 



:■•! 



Navicula gemiviata Grev. 





?^^rs .^f^^>^"'>^i 



X 



1 . 



- O 



^.^ /r n 



^'' ^^ ' v.^:? 



A>' 



Surirella baldjikii Norm. 







Surirella gracilis O'Me. 



