I've also seen some CTB Univega mixtes (probably also made by Miyata) and a couple of butted mixte frames with Nishiki branding.

To the OP: In case you were asking about the frame configuration, rather than the material, that's a mixte frame, identified by the continuous tube connecting the headtube and rear dropouts. They're often confused with "ladies'" bikes, but they're a much sturdier design. And more likely to be ridden as practical city transport by men with confidence in their masculinity. The step-through makes them notably more convenient for those who ride in non-stretch clothing.