How to tell the differences between species in the genus Phigalia found in America?

Fortunately in America, there is only one species of the genus Biston - Biston betularia, and its two subspecies. After identifying Peppered Moths in America for a while, I was thinking of branching out to other species in the Tribe Bistonini.

I noticed on Lycia ypsilon that it looks like European Oak Beauty, Biston strataria, except it has the brown colored regions in reverse.

Cochisea sinuaria may look similar to the Peppered Moth, but it does not have as much maculation, and it has a unique “M” pattern on the dorsal abdomen.

However, when I look at the genus Phigalia, many species look very similar. They are clearly different from the other aforementioned moth species since the postmedial line starts to converge toward the medial line as it goes toward the center of the moth, and they often have a terminal line as well. Is there any expert here on iNaturalist that is able to tell the differences between Phigalia species? And is there one species of Phigalia that is easily distinguishable compared to the others? I am sure other people on iNaturalist are having trouble identifying these species, too.

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Have you tried opening your favorite new book on the Bistonini and flipping to the Phigalia section?

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Thanks for the tip. Yes, I have. But the differences appear very subtle in the iNaturalist pictures, which can appear different based on the light. I guess I just need to practice more.

Was Phigalia the most difficult group for you to distinguish between the various species?