There is hereby established a retirement system for the Mississippi Highway Safety Patrol, as defined in this chapter, effective July 1, 1958, under which members of the Mississippi Highway Safety Patrol may retire for superannuation or may retire for reason of disability, and providing benefits to widows and orphans of such patrolmen. This retirement system is designed to supplement and is in addition to the provisions of Sections 25-11-1 through 25-11-21. Under the terms of this chapter, the highway safety patrolmen, as defined herein, retain all the benefits of old age and survivors insurance under the federal laws administered by the department of public health, education and welfare, or its successor, as provided in the federal and state agreement executed on July 2, 1952, but shall not be eligible for benefits under Sections 25-11-101 through 25-11-139, which is the state retirement annuity plan for state employees. This chapter is a substitute for and in lieu of said sections, and is designed to provide more liberal benefits for the highway safety patrolmen by reason of the dangerous nature of their employment.