East from Great Plains:
A prominent black spot on near the rear of the front wings discal cell
(left of center of the 1st image) can help distinguish this species from the similar Great Spangled Fritillary, in which the same spot is usually absent or small and inconspicuous [there are exceptions in both species]. Great Spangled and Atlantis males usually have very prominent black scaling along the cubital and medial veins
on upper front wing, which is nearly lacking in male Aphrodite. Atlantis usually have much more prominent blackish borders above (especially when comparing males). When alive, male Atlantis have gray eyes (may look slighly bluish), while Aphrodite and Great Spangled have brownish eyes (may look slightly yellowish or reddish, and to some people may appear slightly greenish). Under wing of Great Spangled has broad pale submarginal band, while this band is narrow or sometimes even lacking in Atlantis and Aphrodite.
Speyeria idalia and S. diana both also have brownish eyes, but otherwise cannot be confused with any other species.
Aprhodite differs from S. cybele and S. atlantis in same ways. All other species besides S. nokomis, S. cybele, & S. idalia have gray eyes when alive (except sometimes S. hesperis in parts of Arizona and New Mexico), and all similar species except S. mormonia (which is much smaller and from higher elevation) normally have the strong black scaling along veins of upper front wings of males. Several species always or often have colors other than red-brown on the lower hind wing. S. aphrodite has light spots silvered below, other similar species may not.
Speyeria aphrodite; female - left; male - right; showing black spot below discal cell and lack of black along veins in male:
Speyeria cybele male - left; Speyeria atlantis male - right; for comparison:
Rocky Mountains from British Columbia to Utah and eastward to near east coast in southern Canada and northern U.S. Southward along eastern mountains to northern Georgia.