(a) The Treasurer of State shall be the legal custodian of the securities of the respective retirement systems. However, the systems may deposit with the Treasurer of State, in lieu of securities, safekeeping receipts or evidence of federal bookkeeping entries.
(b) The financial institution or depository issuing the safekeeping receipts, unless issued by an agency of the federal government, shall have on file with the Treasurer of State a letter of the issuer's bonding or insurance company, stating the amount of insurance currently in force covering loss or theft of the securities.
(c) In addition, the boards of trustees of the respective retirement systems, if deemed necessary to facilitate particular investment transactions, the settlement of security transactions, redemption of particular securities, or collection of investment income, may select and designate such banks, trust companies, or central depositories as may be appropriate to act as legal custodian of their securities.