(a) Except as provided by Subsection (c), an eligible surviving spouse who is the designated beneficiary of a person who died before April 8, 1957, and who had at the time of death a total of at least 25 years of service credit and military leave credit in the retirement system, is eligible to receive an applicable survivor benefit available under Section 824.404.
(b) A surviving spouse eligible under this section to receive a benefit is one who has not received from the retirement system a benefit based on the member's death, other than a return of the member's accumulated contributions.
(c) A surviving spouse who qualifies under this section for a survivor benefit is not eligible to receive a lump-sum benefit under Section 824.404(a).
(d) A benefit under this section is payable beginning on the last day of the month in which an eligible person applies for the benefit on a form prescribed by and filed with the retirement system.