Schmidt- and Maksutov-Newtonians are catadioptric telescopes (ie they both use mirrors and lenses).
The optical design of the Schmidt-Newton telescope combines elements from both the Schmidt camera and the Newtonian telescope. In this system the parabolic primary mirror common in newtonian reflector is replaced by a spherical mirror, which introduces spherical aberration. This is corrected by the Schmidt corrector plate, like that used in Schmidt-Cassegrain telescopes. From the Newtonian, it inherits the flat secondary mirror. Source