Wing margin: Are the fringes chequered?
What is meant are contiuous black interruptions of the fringes all the way to the outside. In almost all Blues the outer edge ends with a fringe that is white or brownish. In some, the fringes are interrupted black, occasionally only on the fore-wing or only on the hind-wing. Often this interruption is only hinted at. Some Blues have weak or no fringes, when they are older.