(a) A beneficiary may be designated in accordance with the provisions of sections 90 and 390 of the Retirement and Social Security Law. Each such designation shall be:

(b) A member electing either the five year certain option or the 10 year certain option may designate a primary beneficiary, or a primary beneficiary with a contingent beneficiary. The designation of multiple beneficiaries for the benefits payable under these options is permitted provided, however, the benefits are divided on a per capita basis (share and share alike of those surviving).

(c) Upon the death of a pensioner, the beneficiary of a five year certain or 10 year certain option shall be paid a monthly allowance, equal to the retirement allowance received by the pensioner, for the unexpired period of the guaranteed option, if any. The beneficiary of a pensioner shall not be eligible for a lump sum payment of the benefit. In the event the pensioner shall have designated his estate as beneficiary, or if his designated beneficiary(ies) shall have predeceased him, or he has failed to designate a beneficiary, the commuted value of the payments for the unexpired period of the guaranteed option, if any, shall be paid in a lump sum to the pensioner's estate or in accordance with the provisions of section 1310 of the Surrogate's Court Procedure Act.

(d) A pensioner's beneficiary who is receiving payments under either the five year certain option or the 10 year certain option may designate a primary beneficiary, or a primary beneficiary with a contingent beneficiary. The beneficiary of the pensioner's beneficiary will receive the commuted value of the payments for the unexpired period of the guaranteed option, if any, as a lump sum payment. In the event the pensioner's beneficiary dies without having designated a beneficiary or his beneficiary has predeceased him or he has designated his estate as beneficiary, a lump sum payment in the amount of the commuted value of the benefit shall be made to either the estate of the pensioner beneficiary, or in accordance with the provisions of section 1310 of the Surrogate's Court Procedure Act.