Installing Mac OSX Snow Leopard in Parallels 12

I've been trying to installing an older version of Mac OSX on a machine with Mojave. I've looked around the forums and haven't found a direct solution to my problem. First, I don't see Mac OSX as a free install in the Parallels wizard. Second, when I select install from a DVD is seems to do something till it reports errors presumably while installing from my original Snow Leopard CD? Any ides would be much appreciated. Parallels version: 12.2.1

 

Older versions of OS X did no permit virtualization unless it was a server. I ended up virtualizing Snow Leopard server under VMWare, but have not yet moved it to Parallels.

 

OK, thanks for your help.