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Frustulia crassinervia has prominently undulate valve margins, while the margins of F. inculta are very slighty undulate. In addition, F. crassinervia has a smaller porte-crayon and higher stria density than F. inculta. F. crassinervia has much narrower apices and finer valves than F. quadrisinuata. The valve margins of F. crassinervia are more strongly undulate and its apices more narrowly protracted than those in F. saxonica.

LM scalebar = 10 µm
Frustulia crassinverva LM6 Frustulia crassinverva LM5 Frustulia crassinverva LM4 Frustulia crassinverva LM3 Frustulia crassinverva LM2 Frustulia crassinverva LM1
Length Range
34.5-48.0 µm
Width Range
9.0-10.5 µm
Striae in 10 µm
33-35 in the center

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

Frustulia saxonica

Rabenh. 1850

Frustulia saxonica LM7 Frustulia saxonica LM6 Frustulia saxonica LM5 Frustulia saxonica LM4 Frustulia saxonica LM3 Frustulia saxonica LM2 Frustulia saxonica LM1
Length Range
46.5-87.5 µm
Width Range
12.5-17.5 µm
Striae in 10 µm
30-33