def lookup_continuum_range(continuum_ranges, longitude):
    """
    Lookup the velocity range that shouild be used for measuring the continuum
    levels at a particular longitude.

    :param continuum_ranges: The list of continuum ranges.
    :param longitude: The integer longitude to be checked.
    :return: The min and max continuum velocities.
    """
    if longitude < 0:
        longitude += 360
    continuum_start_vel = -210
    continuum_end_vel = -150
    for row in continuum_ranges:
        if row['min_long'] <= longitude <= row['max_long']:
            continuum_start_vel = row['min_con_vel']
            continuum_end_vel = row['max_con_vel']
    return continuum_start_vel, continuum_end_vel