Source : Free On-Line Dictionary of Computing

Motorola 68050
     
        There was no 68050.  The successor to the {Motorola 68040} was
        the {Motorola 68060}.
     
        The even numbers (68000, 68020, 68060) were reserved for major
        revisions to the 680x0 core.  The odd numbers (68010, 68030,
        68050) were minor upgrades from the previous chip.  For
        example, the {Motorola 68010} was a {Motorola 68000} with some
        minor enhancements and modifications to some user/superuser
        instruction assignments.  The {Motorola 68030} was a {Motorola
        68020} with an {MMU} and more minor enhancements.  The 68050
        would have been a 68040 with some bugs fixed, which didn't
        really warrant a new name so it was sold as a 68040.
     
        (1995-11-29)