In many places, the UK in particular, euphrosyne is considerably less common than the Small Pearl-bordered Fritillary (B. selene). However, in southern France the reverse seems to be true, and in Var and the Alpes-Maritimes selene does not occur so there is never an ID problem. In fact, having visited a variety of locations in southern France in the past six years I have not seen a single selene, and euphrosyne was often common, sometimes very common.

They are superficially quite similar, but selene is usually smaller and often darker and the uppersides can be differentiated by the uph marginal markings - in selene they are slightly sagittate and touching the margins, making them enclosed or "pearls" as this is supposedly how it became named; in euphrosyne the marginal marks are more regular solid triangles not quite touching the margins.

observations

a male, based on body shape/length.

a male, based on body shape/length and the lighter markings (especially in the basal area).

a very heavily marked male, probably an altitude effect.

I'm guessing this is a female based on body shape, backed up by the degree of basal black markings, but I'm not certain at all.

clearly a female based on the shape of the abdomen, but rather dark and suffuse.

probably a male, based on what can be seen of the end of the abdomen. This is fairly typical and shows the redness of the euphrosyne underside quite nicely.

probably a female based on the thickness of the abdomen, but the length may suggest male. The underside is exceptionally red.

an underside, a female based on what I saw of the upperside at the time.