LXVIII.  The union of kindred within the prohibited degrees of marriage, if detected as having taken place in acts of sin, shall receive the punishment of adultery. This Canon is thus interpreted by Aristenus, Matrimonium cum propinqua legibus prohibitum eadem ac adulterium pœna castigatur:  et cum diversæ sint adulterorum pœnœ sic etiam pro ratione propinquitatis tota res temperabitur.  Hinc duas sorores ducenti vii. anni pœnitentiœ irrogantur, ut in adulterio cum muliere libera commisso. non xv. ut in graviore adulterio, or does it mean that incestuous fornication shall be treated as adultery?