Species ofThalassiosira(Diatoms, Bacillariophyceae) in the plankton of English rivers

Abstract
Thalassiosira fluviatilis Hustedt and T. pseudonana Hasle et Heimdal have been found to be widespread in both large and small rivers, while a third taxon, apparently new, has been recorded several times. The appearance of the frustules by light and electron microscopy is commented upon and illustrated, and some of the difficulties of identifying these small diatoms are discussed.