Navicula rhynchocephala Kützing
 
Synonym:
Navicula rhynchocephala var. constricta Hustedt

 Light micrograph from Cape Cod, MA
Contributed by P.A. Siver

 

 
 Scanning electron micrographs from
Avery Pond, CT and Wyassup Lake, CT
Contributed by E.A. Morales