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Frustulia inculta has parallel striae at the apices. In addition, the central nodule of F. amphipleuroides is generally much more elongate than that of F. inculta. Frustulia quadrisinuata has noticeably undulate margins.

LM scalebar = 10 µm
Amphi1 Frustulia amphipleuroides LM1 Amphi4 Amphi5 Amphi3
Length Range
63.0-97.0 µm
Width Range
15.0-16.5 µm
Striae in 10 µm
23-25 in the center, 25-26 at the ends

Frustulia inculta

Siver, Pelczar and Hamilton 2009

Frustulia incluta LM1 Frustulia incluta LM2 Frustulia incluta LM3 Frustulia incluta LM4 Frustulia incluta LM5 Frustulia incluta LM6
Length Range
54-74 µm
Width Range
11.5-14.0 µm
Striae in 10 µm
28-30 in the center valve, 27-28 at the ends

Frustulia quadrisinuata

Lange-Bert. 1996

Frustulia quadrisinuata LM2 Frustulia quadrisinuata LM1 Frustulia quadrisinuata LM5 Frustulia quadrisinuata LM4 Frustulia quadrisinuata LM3
Length Range
58.0-67.0 µm
Width Range
14.0-15.0 µm
Striae in 10 µm
30-31