Abstract
A new aberrant form of Isoteinon lamprospilus C. et A. FELDER, of which white markings of forewing and underside of hindwing are completely disappeared, is found at Mito City of Ibaragi Prefecture of Honshu. In this locality, specimens of this form are abundantly observed mixed with the maculated normal form, and therefore the present form should not be within a usual individual variation, but a distinct mutant.
