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Eunotia naegelii is more narrow and has a greater stria density than E. bilunaris and E. flexuosa.

LM scalebar = 10 µm
Eunotia Naegelii Long I Eunotia Naegelii Long Ii Eunotia Naegelii Long Iii Eunotia Naegelii Mid Eunotia Naegelii Girdle Eunotia Naegelii Short Ii Eunotia Naegelii Short
Length Range
42-180 µm
Width Range
2.5-3.5 µm
Striae in 10 µm
14-17 in the center, 16-22 at the ends

Eunotia bilunaris

(Ehrenb.) Schaarschm. 1881

Eu Bilun 1 Eubilun 8 Eu Bilun 3 Eu Bilun 4 Eu Bilun 5 Eu Bilun 6 Eu Bilun 7
Length Range
33–110 µm
Width Range
3.1–4.7 µm
Striae in 10 µm
11–16 at center of the valve, 15–19 near the apices

Also compare to

Eunotia flexuosa

(Bréb. in Kütz.) Kütz.