I have some SEM photos of diatoms (see attachment) from sandy sediments from the isolation basin at the Baltic Sea coast. These Psammothidium (?) were together with Amphora pediculus, Cocconeis neothumensis, Karayevia clevei, Fragilaria inflata var. istfanffyi, Amphora minutissima and different small fragilarioids. At the beginning it reminded me something like Achnanthes fogedii (which appears later in the same sediment sequence), but it has a different shape. Later I checked it under the SEM, it is not A. fogedii for sure, but I can't find what could it be. 

I would be very grateful if anybody could help me with some ideas.