[mykwyner]

There is some controversy on this topic, but most usage manuals now say "spell it the way you pronounce it." We write, "That is the Joneses' house," because we would pronounce it Jonzez house; we write "...in Jesus's name," because we pronounce it Jezusez name. The consonant cluster at the end of mists's would be nearly impossible to pronounce, so all other rules aside, I would never spell it that way. It is ladyinthemists' website.