Eunotia is a genus of diatoms. They are fresh water diatoms, specifically common in lakes, and they are also common in fossil records, although their siliceous wall design may have been lost and they appear plane, an example is Eunotia tetradon.
^Ehrenberg, C.G. (1837). Über ein aus fossilen Infusorien bestehendes, 1832 zu Brod verbacknes Bergmehl von den Grenzen Lapplands in Schweden. Bericht über die zur Bekanntmachung geeigneten Verhandlungen der Königl. Preuß. Akademie der Wissenschaften zu Berlin 1837: 43-45