Compare

Frustulia magaliesmontana is greater in length (55-70 μm) and is not known to have been reported in North America. Frustulia cassieae is also larger and has apices that are not protracted.

LM scalebar = 10 µm
Frustulia pseudomagaliesmontana LM5 Frustulia pseudomagaliesmontana LM4 Frustulia pseudomagaliesmontana LM6 Frustulia pseudomagaliesmontana LM2 Frustulia pseudomagaliesmontana LM3 Frustulia pseudomagaliesmontana LM1
Length Range
30-45.7 µm
Width Range
5.8-6.2 µm
Striae in 10 µm
40-42

Also compare to

Frustulia magaliesmontana

Cholnoky

Frustulia cassieae

Lange-Bert. and Beier