50 



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 



Fig. 66. Achnanthes brevipes , (5), cells 20-125u long, 12-30u wide; 

 coarsely punctate. X 1000. 



rapheless valve 



girdle view 

 Notes : 



raphe -bearing valve 



Fig. 67. Achnanthes flexella , (ll), cells 20-80u long, 10-26u wide; 

 sigmoid raphe. X 1500. 



raphe -bearing valve 

 Notes : 



rapheless valve 



