Penalty for undisclosed income: a ten per cent additional penalty applies where income is determined as unexplained, subject to declared income exemption. A special penalty permits the assessing authority to direct payment of an additional penalty equal to ten per cent of the tax chargeable under the specified tax provision where income is determined as undisclosed or deemed income; amounts already declared in the return with the specified tax paid by the end of the relevant year are exempted from this penalty.