The SUBCLUB lists the Merlin, of course, but the OP asked about 16mm cameras.
(1936) The Merlin was an early, odd-looking, cast-iron submini. It was made by the United Optical Instrument Company in England, and was one of the first attempts to make a viable small camera. But actually, there were several other subminis of the same period that had similar, odd film styles and body shapes. The Merlin came in three colors -- black, blue or green -- and produced 20x20mm images. The film was loaded into tiny cassettes that resemble 35mm cassettes (which didn't even exist at the time). The camera was tiny -- only two inches wide -- and very basic. It had a pop-up viewfinder, a single speed shutter and an f16 lens. There was a small "ruby" window on the back to read the film exposure number on the back of the paper-backed film. The Merlin was also used as the "guts" of the Erac Pistol Camera.
These 16mm negatives were obviously exposed in a non-16mm PRE-WWII camera -- not only because there were so few PRE-WWII 16mm cameras, but because of the exposed perforations. Could it have been a Merlin? Sure, but I'd put my money on a more commonly available and commonly used camera of the time.