32 



Other species of COSCINODISCUS. 



8a True raphe present on at least one valve; raphe may be 

 very short or rudimentary, or may be concealed in a keel 

 or wing 



8b True raphe absent, pseudoraphe present on both valves. 



15 

 9 



9a Frustules with thick longitudinal septae running parallel 

 to the valve face - TABELLARIA . 



Fig. 3^- Tabellaria fene strata, (3), cells 30-l^Ou long, 3-9U wide; 

 18-20 striae in lOuJ^-S intercalary bands per cell. In 

 Great Lakes and Columbia River. 



septum 



girdle view. X 1000 



C= 



0= 



=o 



Colony 



X 250 



valve view. X 1000 



Notes : 



