def return_agar_plates(wells=6):
    """Returns a dict of all agar plates available that can be purchased.

    Parameters
    ----------
    wells : integer
        Optional, default 6 for 6-well plate

    Returns
    -------
    dict
        plates with plate identity as key and kit_id as value

    Raises
    ------
    ValueError
        If wells is not a integer equaling to 1 or 6

    """
    if wells == 6:
        plates = {"lb_miller_50ug_ml_kan": "ki17rs7j799zc2",
                  "lb_miller_100ug_ml_amp": "ki17sbb845ssx9",
                  "lb_miller_100ug_ml_specto": "ki17sbb9r7jf98",
                  "lb_miller_100ug_ml_cm": "ki17urn3gg8tmj",
                  "lb_miller_noAB": "ki17reefwqq3sq"}
    elif wells == 1:
        plates = {"lb_miller_50ug_ml_kan": "ki17t8j7kkzc4g",
                  "lb_miller_100ug_ml_amp": "ki17t8jcebshtr",
                  "lb_miller_100ug_ml_specto": "ki17t8jaa96pw3",
                  "lb_miller_100ug_ml_cm": "ki17urn592xejq",
                  "lb_miller_noAB": "ki17t8jejbea4z"}
    else:
        raise ValueError("Wells has to be an integer, either 1 or 6")
    return (plates)