It looks like a Canon FL mount to me. The aperture pins could be rather long on third party FL mount lenses. Lack of signaling pins means metering could only be done in stop-down mode and fully manual exposure control. The FL mount, introduced in 1964, had a rotating breech ring at the rear of the lens. The lens was aligned with the camera with the ring twisted to the "open" position, then only the ring was rotated to lock it down.

The FD mount followed in 1971. It added signaling pins to the FL mount to communicate the lens' full aperture and set aperture to the camera body. This allowed "automatic" metering with the aperture wide open. Older FL lenses could be used on new FD mount cameras in manual only mode.

From 1971 to 1979 Canon's FD lenses also had a rotating breech ring at the rear of the lens. In 1980 Canon shifted to a "new" FD mount design that kept the ring in a fixed position relative to the lens and the entire lens was twisted to mount or unmount it from the camera. But either style, breech mount ring or bayonet, would work on FD mount camera bodies, and some third party lensmakers continued to make lenses for FD mount cameras with rotating breech rings.

Above we see three generations of the FL/FD mount from Canon. On the left is an FL mount 55mm f/1.2. In the center is a breech-lock FD 55mm f/1.2. On the right is a bayonet style FD 50mm f/1.2 L.