The Canon Pellix came out in 1965, and even though it doesn't have the letter in its name, it's part of their F-series cameras. It was the third in the series (behind the FX and FP), but the first to have through-the-lens (TTL) metering.
It got its name (very few Canon SLRs are named, most get number or letter designations) from the "pellicle" mirror inside, which is what made the camera unique. SLRs work on the principle that the photographer sees the same image that passes through the taking-lens, so what you see is what you get. This is accomplished by putting a mirror at a 45° angle between the rear of the lens and the shutter. The mirror has a hinge and a spring mechanism that lifts it up and drops it back into position. When focusing and composing, the mirror is down and the photographer and set up the shot. When he fires the shutter, the mirror swings up and out of the way, the shutter opens, and light can pass directly from the lens to the film. Then the shutter closes and the mirror drops back down into position. Pretty much all SLRs, even my old Graflex, use this principle.
There are a bunch of drawbacks to this arrangement, however. First is that when the mirror swings up out of the way, the viewfinder goes dark and the photographer can't see anything until the shutter is fired and the mirror drops back down. On fast shutter speeds the dark time is short, but with longer shutter speeds the dark time is annoyingly long, so the photographer is never 100% certain what he shot. Then there's the the fact that the mirror action is very loud. Cameras with leaf shutters are typically very quiet and discreet, but SLRs clatter when the shutter fires. Part of it is the shutter, but some of it is the mirror.
So Canon experimented by putting in a beam-splitting, stationary mirror. Part of the light bounces up through the viewfinder, part passes back to the film plane. The mirror never moves so there's no vibration, no clatter, and especially no black-out when the shutter fires. Great idea.
But it didn't catch on. Beam-splitters mean less light goes to the viewfinder, which makes focusing harder and the image less crisp, and it means slower shutter speeds or larger apertures for exposure. The camera sold but not enough to incorporate the feature into later models (though it's now used in the modern high speed EOS cameras, where shots can be taken much faster because you don't have to wait for the mirror to flip up and down, or have dark-time while the mirror is up.
I have a black-bodied version which I believe is rare: Pellixes were not big sellers in any style, and I didn't know they'd made a black-body variant at all until I saw the one I bought. I have yet to see another one.
Now Canon actually considers that there are two different Pellix cameras, the first version and the QL version; mine has the QL badge so it's obviously the latter. Canon did that a lot with various cameras. The main difference is that mine has the quick-load QL feature, which is nice. I'm told that it is also has some changes to accommodate Canon's Meter Booster.
I was listening to Camerosity Podcast #18: Canon Rangefinders with Peter Kitchingman, and even though it's 90% about Canon's top-tier rangefinders (not the Canonet series), there was a mention about the problems of focal plane shutters in rangefinder cameras: if the lens cap is off and the lens is focused to infinity, and if the lens catches the direct sun, the lens focuses the sun to a small point and can burn holes into the shutter. It depends on the material and the amount of exposure, but pinholes focal plane shutters are a problem in old Canon rangefinders. .
I knew about that, but it had never occured to me that the same thing can happen to a Pellix. The Pellix has the advantage of the pellicle mirror beam-splitting part of the light off into the viewfinder, but it's still something to think about.
Another bit of Pellix trivia that I had not known: because the Pellix's mirror doesn't travel, there's a little more wiggle room between it and the back of the typical Canon FL lens, so Canon made a 38mm ƒ/2.8 FLP lens that could only be used on the Pellix, because the rear element sat back closer to the mirror; on any other FL-mount camera, the mirror travel would hit the lens. Canon dusted off the concept decades later when they introduced the EF-S mount lenses which worked only with APS-C sensor digital cameras, which also had smaller-than-full-frame mirrors. As far as I know, that is the only FLP lens they made.
One last comment: there are two other things that make this camera very unusual for a Canon product: the first is that it's named (Canon often named its rangefinders or point-n-shoots, but almost never named its SLRs). The other is the location of the name. Almost all Canon cameras have the Canon name on the prism (in the center of the camera over the lens) and the model designation on the camera's right-hand side (on the left if you're viewing it from the front). But the Pellix has the name on the prism and the Canon logo on the side. You wouldn't see that again until the T-series cameras (like the T-70) came out twenty-years later—and even then the Canon logo stayed on the prism.
For more information: Canon Camera Museum
Modern Photography magazine camera test: August 1966
Modern Photography magazine "Camera Collector" article: September 1980
One of Modern Photography's Top Cameras
Camera manual: Orphan Cameras.com