§ 490-a. Creation of fund. Any fifty or more credit unions organized under the provisions of this chapter whose share liabilities aggregate not less than fifty per centum of the total share liabilities of all credit unions so organized may enter into an agreement, subject to the approval of the superintendent, to create a fund and from time to time make contributions thereto in accordance with the terms of such agreement, for the purpose of insuring the shares of such credit unions as shall become parties to such agreement; provided, however, that the shares so insured of any one holder in any one credit union shall not exceed two thousand dollars. Such an agreement once entered into may be continued, notwithstanding the fact that any number of associations may cease to be parties thereto.