21 



Fig. 6. Melosira islandica, (3), valves 7-27U in diameter, 

 4-21u long; striae on valve mantle parallel to 

 pervalvar axis. X 1000. Common in the Great Lakes 

 and the Columbia River. 



nm 



Notes : 



girdle view, 

 subsp. helvetica 



Fig. 7. Melosira italica , (3), valves 5-28u in diameter, 8-21u 

 long; differentiated from M. ambigua by more robust 

 spines and narrow sulcus. X 1000. Common in the 

 Columbia River. 



valve view 



girdle view^ 

 var. valida 



Notes : 



Fig. 8. Melosira varians , (3), valves 8-35(i in diameter, 9-13H 

 long; no visible ornamentation. X 1000. Widely distri- 

 buted. 



T 



JL 



valve view 



girdle view 



Notes 



