Well there you have it: "Pentex" for K mount, and "Pentax" for M42. Except there are Pentax K mounts as well.
The Pentax brand is an old brand.
Actually it is neither - according to the OP it is labelled: "Asahi Opt. Co. - Super-Takumar 1:1.8/55"
The OP understood that to mean a Pentax lens when he made his opening post.