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Melanargia lachesis
This species replaces the Marbled White, Melanargia galathea, in the Iberian Peninsular. There appears to be a small overlap between the two species, although I don't know if they ever occur in exactly the same places. The principal difference between the two is the presence or absence of extensive black basal markings on the uppersides. There are many other features too.
I think it is the other one and more common one in Portugal: Melanargia lachesis. For russiae there is a tranversal black band missing on the forewing. But you are exactly at the range border for both species. Russiae would be more in the south of Portugal.