The valval shapes of 314 male Nearctic Limenitis (including 15 samples from nine localities and 20 laboratory-bred hybrids) were examined for anatomical differences. Seven phenotypically different forms are included as follows: L. arthemis, astyanax, the intergrade form proserpina, L. archippus, the rare hybrid form arthechippus, L. lorquini, and L. weidemeyerii. The claspers of each specimen were dissected, mounted on slides, and photographed. Counts and measurements were made of eight larval characters (including four apical features: the number of distal teeth, distal width, and dorsal and ventral angles, as well as four basal traits: valval length and base, and the length and basal width of the inner process), and right forewing length. The data were compared between and among samples by canonical analysis and by one-way analysis of variance tests. Forms of the arthemis–astyanax complex possess no obvious morphological differences in their valvae. The apical characters are constant throughout the group, although the basal valval traits and forewing length show variation in size which is inversely correlated with latitude. The similarity of valval structure in these forms is evidence that they are conspecific. Consistent differences in the apical shapes and valval characters of arthemis, archippus, lorquini, and weidemeyerii confirm that they represent valid species. The valvae of the hybrid form arthechippus are intermediate between the two parental types. The relationships of valval structure to hybridization and genetic isolation are discussed, and consideration is given to the probable evolutionary affinities of the common forms, and how they may have arisen.