A. The board of trustees may deny the right to become members to any class of teachers whose compensation is only partly paid by the state or who are serving on a temporary or other than per annum basis, and it may, also in its discretion, make optional with members in any such class their individual entrance into system.
B. The board of trustees, upon the application of a member who because of his employment is required to become a member of the United States Civil Service Retirement System, shall release from membership in this system said member and shall refund his accumulated contributions.